Patent Application
20230221217
The invention belongs to the fields of microbiology, public health and methods for analysing air ecosystems, in particular to methods and devices useful for collecting air samples and analysing the airborne microbiota present in them. These methods allow to gain a global view of the airborne biological communities as well as to identify pathogens (viruses, bacteria or fungi), allergens and the like present in them.
Air pollution is known to be a major environmental risk to public health. In addition to inorganic pollution, air also carries several airborne biological particles (ABPs) containing archaea, bacteria, virus, fungi and pollen grains, coming from other environments (soil, water or plant/animals microenvironments). A great effort is being made by the international community to reduce air pollution but very little is known about the biological community (airbiota) present in the outdoor air. The study of the airbiota is relevant due to its potential role in dissemination of plant, animal and human diseases, with important implications in public health, and a huge economic impact on crops and stockbreeding productivity. The current knowledge about air microbial community is mainly restricted to pollen and fungal spores, studied using traditional methods such as optical microscopy or quantitative PCR, which because of its importance as allergens are daily measured and included among air quality indicators. Culture-dependent techniques were also used for the study of air microorganisms (fungi, bacteria and viruses), despite the small fraction of organisms that can be cultured. Furthermore, studies on viruses are almost inexistent. Therefore, a global overview of the airborne biological community is crucial to understand air ecosystem dynamics, to identify marker organisms and to establish new air quality indicators. However, there is not a standardized method to capture the whole diversity present in the air.
The interest in the study of airborne microbiota is increasing to understand the connectivity of different ecosystems, the survival of microbes in the air ecosystem and the transmission of human pathogens. In spite of its relevance, the characterization of microbiota in the air is in its infancy. A variety of sampling devices are being used by the research laboratories that have initiated these studies, but detailed studies on the performance of these devices are scarce.
Some of the airborne microorganisms are the causative agent of important human diseases such as Influenza virus, Rhinoviruses, Mycobacterium tuberculosis or Aspergillus spp. Others, although non-pathogenic, are known to act as allergens, such as grass pollen or Alternaria spores, affecting to several million people worldwide. Traditionally, air was considered mainly as a dissemination path for these microorganisms, being studied primary for its important implications in human health and livestock and agriculture productivity. However, in recent studies, the scientific community has suggested that air has its own biota, and thus, must be considered as an ecosystem in itself. Nevertheless, very little is known about airborne biological community, the dynamics governing them or the potential relations among microorganisms and the influence of environmental factors on its composition.
Next-generation sequencing (NGS) is a promising approach to study global microbial diversity that is being applied to other ecosystems such as ocean, freshwater bodies or thermal springs (Rastrojo A., Alcamí A., 2018, Adv Virus Res, 101:39-54; Rastrojo A., Alcamí A., 2017, Virus Res, 239:87-96). NGS was also applied to the study of air communities, mainly through targeted metagenomics of marker genes, but most of the studies were focused on a single group of organisms, mainly bacteria, or only on a couple of groups (fungi and bacteria) (Núñez A., et al., 2016, Int Microbiol, 19:1-13). Among airborne microorganisms, viruses have received little attention. Although there are many studies on specific viruses, such as Influenza virus, only one report has characterized the global viral diversity in outdoor air (Whon T W., et al., 2012, J Virol 86:8221-8231). Moreover, to date, only a few studies have used a shotgun sequencing approach to study whole airborne community, including viruses (Cao C., et al., 2014, Enviromental Science and Technology, 48:1499-1507; Be N. A. et al., 2015, Microb Ecol 69:346-355; Yooseph S., et al., 2013, PLoS One 8:e81862).
A number of devices with very different capture mechanisms have been used to study the airborne community (Núñez A., et al., 2016, Int Microbiol, 19:69-80). Therefore, the evaluation of different capturing methods is required to establish a standarized framework. It has been previously demonstrated that Hirst-type samplers are a good choice for monitoring the airborne biological community, by comparing classical approaches such as optical microscopy of pollen and fungal spores with targeted metagenomics, resulting in a good correlation between both techniques (Nunez A., et al., 2017, Appl Environ Microbiol, 83). Although Hirst samplers can give a good description of the airborne biological community, it is far from being complete. Viruses cannot be studied by targeted metagenomics using marker genes such as 16S/18S rRNA and others approaches are required. Hirst samplers are based on the inertial capture of ABPs in a vaseline covered strip that can be used for DNA extraction. A shotgun sequencing of this DNA could give a more complete view of the airborne community including DNA viruses. However, viral genomes are represented in a very low proportion of sequencing reads in a shotgun approach due to their small genomes compared to cellular genomes. Viral particles should be purified to obtain a complete analysis of the viral community (both DNA and RNA viruses), and this cannot be done from the vaseline strip without introducing some important biases (Prussin A J., et al., 2014, FEMS Microbiol Lett, 357:1-9; Thurber R V., et al., 2009, Nat Protoc 4:470-483). Additionally, Hirst-type samplers are expensive devices and usually not portable, so its usage is limited to a restricted number of sampling sites simultaneously.
Polytetrafluorethylene (PTFE) filters have been also tested for collecting airborne bacteria, virus and other particles in the 10-900 nm size range (Nancy C. B., et al., 2007, Ann. Occup. Hyg., 51: 2, 143-151), however, no efficient analysing method has been proposed for identifying the whole captured biological particles.
Therefore, there is a need for developing improved capturing and analysing methods which use devices and methodologies that allow to collect and study the whole airborne biological community, including viruses and other important pathogens and allergens, in an efficient way.
The document of Booth et al, “Detection of Airborne Severe Acute Respiratory Syndrome (SARS) Coronavirus and Environmental Contamination in SARS Outbreak Units” discloses that severe acute respiratory syndrome (SARS) is characterized by a risk of nosocomial transmission; however, the risk of airborne transmission of SARS is unknown. During the Toronto outbreaks of SARS, we investigated environmental contamination in SARS units, by employing novel air sampling and conventional surface swabbing. Two polymerase chain reaction (PCR)-positive air samples were obtained from a room occupied by a patient with SARS, indicating the presence of the virus in the air of the room. In addition, several PCR-positive swab samples were recovered from frequently touched surfaces in rooms occupied by patients with SARS (a bed table and a television remote control) and in a nurses' station used by staff (a medication refrigerator door). These data provide the first experimental confirmation of viral aerosol generation by a patient with SARS, indicating the possibility of airborne droplet transmission, which emphasizes the need for adequate respiratory protection, as well as for strict surface hygiene practices. Samples were collected on a polytetrafluoroethylene (PTFE; “Teflon”) membrane filter with a pore size of 0.3 μm in a closed-face, 3-piece disposable plastic cassette by use of a personal sampling pump operating at ˜2 L/min. This resulted in the collection of samples that were dry. Samples were shipped with ice packs and refrigerated upon receipt at the laboratory. In this publication, all 28 air samples collected with PTFE filters were negative for SARS by PCR. The only 2 samples that were positive were collected with a different devise (a high-resolution slit-sampler system designed by Defense Research and Development Canada).
The document of [PO YING CHIA et al “Detection of air and surface contamination by SARS-CoV-2 in hospital rooms of infected patients”, NATURE COMMINICATIONS, vol. 11, no. 1, 29 May 2020] discloses that Understanding the particle size distribution in the air and patterns of environmental contamination of SARS-CoV-2 is essential for infection prevention policies. Here we screen surface and air samples from hospital rooms of COVID-19 patients for SARS-CoV-2 RNA. Environmental sampling is conducted in three airborne infection isolation rooms (AIIRs) in the ICU and 27 AIIRs in the general ward. 245 surface samples are collected. 56.7% of rooms have at least one environmental surface contaminated. High touch surface contamination is shown in ten (66.7%) out of 15 patients in the first week of illness, and three (20%) beyond the first week of illness (p=0.01, χ2 test). Air sampling is performed in three of the 27 AIIRs in the general ward and detects SARS-CoV-2 PCR-positive particles of sizes >4 μm and 1-4 μm in two rooms, despite these rooms having 12 air changes per hour. This warrants further study of the airborne transmission potential of SARS-CoV-2. In D2 it is disclosed that Six NIOSH BC 251 bioaerosol samplers were placed in each of three AIIRs in the general ward to collect air samples (set-up depicted in Supplementary
The document of [K K COLEMAN et al, “Bioaerosol Sampling for Respiratory Viruses in Singapore's Mass Rapid Transit Network”, SCIENTIFIC REPORTS, vol. 8, no. 1, 30 Nov. 2018] discloses a UV-sterilized Biological Safety Cabinet Class II and sterile consumables, and equipment were used to process samples. Using a filter-handling kit (225-8372; SKC), each polytetrafluoroethylene (PTFE) filter was removed from the NIOSH sampler cassettes and transferred to a 50 mL Falcon tube and vortexed while dry for 5 seconds. To minimize cross-contamination, forceps were sterilized with 70% ethanol in between each filter transfer. One millilitre of 0.5% BSA solution was then added to each 50 mL Falcon tube containing a filter and vortexed again for 15 seconds. One millilitre of 0.5% Bovine Serum Albumin (BSA) solution was added to each 1.5 mL conical tube from the NIOSH samplers and vortexed for 10 seconds. Using cryotube vials, the BSA solutions from the 50 mL Falcon tubes containing filters were pooled together with their respective 1.5 mL conical tube sample. Two millilitres of BSA solution were added to each 15 mL Falcon tube from the NIOSH samplers, vortexed for 15 seconds, and transferred to cryotube vials. In this publication, it is mentioned that ‘prior to molecular analysis, the particles collected in the 1-4 μm and <1 μm size fractions were combined’. Therefore, a virus-positive results does not demonstrate that the PTFE filter (<1 μm size) was able to capture the virus, since it may have been retained in the previous tube (1-4 μm size). Also, this publication shows positive results for influenza virus, adenovirus and RSV, but not for coronavirus (see Table 1).
The document of [T. A. MYATT “BMC Public Health Airborne rhinovirus detection and effect of ultraviolet radiation on detection by a. semi-nested RT-PCT assay”, 13 Jan. 2003] discloses an experiment with aerosolized rhinovirus in a small aerosol chamber. Experiments were conducted with decreasing concentrations of rhinovirus. To determine the effect of UV irradiation on detection of rhinoviral aerosols, we also conducted experiments in which we exposed aerosols to a UV dose of 684 mJ/m2. Aerosols were collected on Teflon filters and rhinovirus recovered in Qiagen AVL buffer using the Qiagen QIAamp Viral RNA Kit (Qiagen Corp., Valencia, Calif.) followed by semi-nested RT-PCR and detection by gel electrophoresis. In this publication Teflon filters used had a 2 μm pore, and the rhinovirus detected was generated with a nebulizer in the laboratory—
The document of [T. A. MYATT “Detection of Airborne rhinovirus detection and its relation to outdoor air supply in office environments”, AMERICAN JOURNAL OF RESPIRATORY AND CRITICAL CARE MEDICINE, vol. 169, no. 11, 1 Jun. 2004] discloses an experiment wherein weekly air samples were collected in two centralized locations in each study area from 9 a.m. to 5 p.m. on workdays at 4 L/minute with closed-faced cassettes on 37-mm Teflon filters (Teflon 2.0 μm pore; Pall Gelman, Ann Arbor, Mich.). The filters were placed approximately 1 m from and horizontal to the floor (23). The closed-faced cassettes prevented direct contact with occupants and limited the chance that large droplets would be collected. We prepared weekly field and laboratory blanks and outdoor background samples. Filters were stored at −80° C. until analysis. This publication used Teflon filters of 2 μm pore size, and detected only rhinovirus, not coronavirus, in an office environment.
The document of [K. ROSARIO et al. “Diversity of DNA and RNA viruses in Indoor Air As assessed via Metagenomic Sequencing” ENVIRONMENTAL SCIENCE & TECHNOLOGY, vol. 52, no. 3, 23 Jan. 2018] disclose that diverse bacterial and fungal communities inhabit human-occupied buildings and circulate in indoor air; however, viral diversity in these man-made environments remains largely unknown. Here we investigated DNA and RNA viruses circulating in the air of 12 university dormitory rooms by analysing dust accumulated over a one-year period on heating, ventilation, and air conditioning (HVAC) filters. A metagenomic sequencing approach was used to determine the identity and diversity of viral particles extracted from the HVAC filters. We detected a broad diversity of viruses associated with a range of hosts, including animals, arthropods, bacteria, fungi, humans, plants, and protists, suggesting that disparate organisms can contribute to indoor airborne viral communities. Viral community composition and the distribution of human-infecting papillomaviruses and polyomaviruses were distinct in the different dormitory rooms, indicating that airborne viral communities are variable in human-occupied spaces and appear to reflect differential rates of viral shedding from room occupants. This work significantly expands the known airborne viral diversity found indoors, enabling the design of sensitive and quantitative assays to further investigate specific viruses of interest, and providing new insight into the likely sources of viruses found in indoor air.) This publication does not use PTFE filters, but air conditioning HVAC filters.
The document of [YI YU LAI et al. “Metagenomic Human respiratory air in a hospital environment, PLOS ONE, vol. 10, no. 10, 2 Oct. 2015] discloses that all samples were collected in Beijing Hospital (Google Marker location: 39° 54′3.5”, 116° 25′0.78″), details of the room conditions were listed in Table 3. We set up an air sampling pump (SKC, PA, US) and connected to a 47 mm filter holder (PALL, NY, U.S.) by TYGON tube (Saint-Gobain Corporation, US), with a 47 mm, 0.2 um PTFE Membrane filter (PALL, NY, U.S.) inside.
Finally, the document U.S. Ser. No. 10/663,454B2 discloses a handheld air sampler device for enrichment of airborne substances and/or particles, in particular microorganisms, includes: an inlet configured for air intake into a flow channel; an outlet configured for fluidic ally connecting the flow channel to an external vacuum device; a permeable backing element arranged in the flow channel, the backing element being configured to receive and support a filter element; and a sealing element configured for sealing a filter element received on the backing element such that, when a negative pressure is applied to the outlet, air entering the inlet forms an airstream passing the filter element and airborne substances and/or particles, in particular microorganisms, are enriched in the filter element. An air sampling arrangement includes a handheld air sampler device of this type. This publication describes a pipeline to process clinical samples, but it is not focused on viruses present in air samples, nor described an air sampler to capture viruses. This publication does not detect viruses (see
In front of the prior art documents, the present invention improves the collection of viral particles in the air. Consequently, the objective technical problem that the invention solves is to provide a device form improving the collection of viral particles in the air. The claimed solution comprises the synergistic effect between a PTFE filter with a pore size of 1 μm or 5 μm and coupled with a processor operable to enable the air to flow through or over the substrate, thereby causing the particles in the air to be captured by the substrate, centrifugal means configured to remove cellular organisms from the substrate; buffering means configured to house the substrate, and filtration means configured to filtrate the supernatants containing the virus particles, wherein the centrifugal means are also configured to concentrate the supernatants.
The present invention refers to a device for capturing air biological particles which comprises polytetrafluorethylene (PTFE) filters and its use for collecting, detecting and identifying organisms present in air ecosystems. The invention also provides a method suitable for the capture, detection and identification of whole airborne biological particles, including viruses and other important air pathogens and allergens, with the use of the device comprising the PTFE filters and preferably a sequencing shotgun metagenomic approach. This method allows to perform organism, preferably viral, metagenomics to sequence all DNA and RNA organisms captured in the filters, and/or to amplify specific genomes by gene amplification methods. This methodology may be applied to detect, for instance, SARS-CoV2 particles in air samples.
The study of the airborne biological community, composed by very different organisms (such as bacteria, fungi, pollen and virus), requires the use of an efficient sampling method that captures a good representation of the whole community. In the present invention, inventors have analysed the microbial community captured with seven different air samplers, based on different capturing methods (impact samplers, cyclonic, impinger and filters), to determine which is the most suitable to obtain a more complete view of the airborne biological community and to establish it as a standarized method.
Thus, in the present invention different methods for collecting airborne microorganisms, including impactor samplers, liquid impingers, cyclonic samplers and different filters, have been tested. Additionally, to avoid the biases of culture-dependent methods or amplicon-based analyses, the inventors have performed a next generation sequencing (NGS) shotgun approach to uncover the whole airborne diversity. A detailed analysis of the genetic diversity of the airbiota captured using these different methodologies is presented in the Examples shown below. Therefore, the Examples of this application provide a detailed comparison of the biodiversity detected by seven different air sampling devices, with the analysis of shotgun metagenomics and amplicon sequencing of prokaryotic/eukaryotic organisms to evaluate the biodiversity captured by the different samplers. The results obtained evidence that, while isolation and purification of virus particles is not possible from many devices, PTFE filters are the best option for capturing and analysing viral metagenomics and thus these filters are the methodology of choice for performing the most efficient sampling and analysing method that captures the best representation of the whole airborne organisms community.
Consequently, the Examples shown below, which compare airbiota analysis from different air samplers, evidence that PTFE filters show the best efficiencies capturing microbial diversity from the air (
PTFE filters have also the following advantages: they are cheaper than others samplers, replicates can be sampled using two or more filter holders, and several localizations (both outdoor and indoor) can be studied simultaneously using several devices with a reduce cost. Additionally, taking into account other factors such as cost and portability, PTFE filters were the most convenient device of those tested. Finally, it has been demonstrated herein that PTFE filters allow the extraction of the viral fraction for viral metagenomics, which allows the analysis of the whole airborne biological community. Consequently, PTFE filters represent the best option for performing viral metagenomics because of the easy to extract cellular organism and virus particles by shaking or sonication of the filters in a buffer.
Therefore, in a first aspect, the present invention relates to a device for capturing air biological particles, hereinafter “the device of the invention”, comprising:
wherein the substrate and the at least one processor are communicatively coupled.
Preferably, the substrate comprises at least one filter acting as the at least one captor.
Preferably, the at least one filter is a polytetrafluorethylene (PTFE) filter.
Preferably, the polytetrafluoroethylene (PTFE) filter is a synthetic fluoropolymer of tetrafluoroethylene filter.
In a preferred embodiment of the device, the PTFE filter has a nominal pore size between 0.2 μm and 5 μm, preferably 1 μm or 5 μm, more preferably of 1 μm. A PTFE filter with a nominal pore size of 1 μm is specially advantageous for collecting viral particles from air.
Optionally, the device for capturing air biological particles further comprises an air pump operable to increase or decrease flow of air,
wherein, to capture the particles into the substrate, the at least one processor is operable to:
cause the air pump to increase or decrease the flow of air containing the particles toward the substrate.
Preferably, the air pump is a vacuum pump.
Another aspect refers to the use of the device of the invention for collecting or capturing or sampling, and for detecting and identifying organisms present in air (including outdoor and indoor air), preferably wherein the detection and identification are performed by metagenomic analysis, more preferably by a sequencing shotgun metagenomic approach. Alternatively, by amplification of specific genomes with the use of specific primers and gene amplification methods, followed by sequencing.
The invention also refers to a system for detecting and identifying organisms present in the air comprising the above explained device for capturing air biological particles.
Preferably, the system for detecting and identifying organisms present in the air further comprises centrifugal means configured to remove cellular organisms from the substrate, and buffering means configured to house the substrate.
Preferably, the system for detecting and identifying organisms present in the air further comprises filtration means configured to filtrate the supernatants containing the virus particles, wherein the centrifugal means are also configured to concentrate the supernatants.
Preferably, the system for detecting and identifying organisms present in the air further comprises nuclease treatment means configured to remove all non-encapsidated DNA or RNA.
Preferably, the system for detecting and identifying organisms present in the air further comprises gene amplification and sequencing means for the amplification of collective or specific viral genomes captured in the filters, followed by sequencing.
In another more preferred embodiment, the detection and identification of organisms present in air, referred to in the present invention, is performed by metagenomic analysis, more preferably by a next generation sequencing (NGS) shotgun approach.
In another more preferred embodiment, for sequencing and detection of specific viruses, the viral genomes or a specific gene are amplified by PCR with specific primers and the product is identified by quantitative (qPCR) or quantitative reverse transcription PCR (RT-qPCR), or sequenced using Illumina HiSeq 200 machine or equivalent.
In another preferred embodiment the system for detecting and identifying organisms present in the air comprises the device of the invention and further comprises centrifugal means configured to remove cellular organisms from the substrate, buffering means configured to house the substrate filtration means configured to filtrate the supernatants containing the virus particles, wherein the centrifugal means are also configured to concentrate the supernatants, nuclease treatment means configured to remove all non encapsidated DNA or RNA and gene amplification and sequencing means for the amplification of collective or specific viral genomes captured in the filters, followed by sequencing.
The organisms present in air or in air samples will be also referred to in the present invention as “airborne organisms”, “airbiota” or “airborne biological community”. These organisms are, preferably, microorganisms, more preferably, the organisms are selected from the list consisting of: viruses, including DNA and RNA viruses, plants, bacteria, pollen and fungi. Even more preferably, the organisms are air pathogens, particularly viruses, preferably SARS-CoV2.
“Air pathogens” are those organisms present in the airbiota which are capable of trigger a disease, an infection, a clinical condition, and the like, in humans or non-human animals. Examples of “air pathogens” are, but without limitations, bacteria such as Mycobacterium tuberculosis, Bordetella pertussis and Mycoplasma pneumoniae, and viruses such as influenza virus, coronavirus, adenovirus, varizela zoster virus and respiratory syncitial virus.
Thus, another aspect of the invention refers to the use of the device of the invention for collecting, detecting and identifying air organisms, hereinafter “the use of the invention”.
In a preferred embodiment of the use of the invention the air organisms are selected from the list consisting of: viruses, plants, bacteria, pollen and fungi.
In another preferred embodiment of the use of the invention the organisms are air pathogens, preferably virus pathogens, more preferably the virus is SARS-CoV2.
Another aspect of the invention refers to a method, hereinafter “the method of the invention”, for collecting, detecting and identifying organisms, preferably microorganisms, present in the air, or for the analysis of airbiota, wherein said method comprises the steps of:
The sampling of step (a) may be performed during at least 1 hour, preferably at least one day, more preferably during at least 4 consecutive days, even more preferably during at least 8 consecutive days, even more preferably during at least 12 hours per day.
The genetic material of step (b) may be DNA or RNA, single or double stranded, circular or lineal. This genetic material may be extracted by conventional DNA or RNA extraction methods well-known in the art.
Amplification of step (c) is preferably carried out by multiple displacement amplification (MDA), more preferably using primers for 16S rRNA, for bacteria, and Internal transcribed spacer 2 (ITS2), for plants and fungi.
In another preferred embodiment, the metagenomics analysis of step (d) is performed by an NGS shotgun approach, more preferably using an Illumina HiSeq 2000 machine or equivalent.
In another preferred embodiment, the method of the invention comprises an alternative step c (c′) by amplification of specific genomes with the use of specific primers and gene amplification methods, followed by sequencing.
For sequencing and detection of specific viruses of step (c′), the viral genomes or a specific gene are amplified by PCR with specific primers and the product is identified by quantitative (qPCR) or quantitative reverse transcription PCR (RT-qPCR), or sequenced using Illumina HiSeq 200 machine or equivalent.
In another preferred embodiment of the method of the invention, the organisms are selected from the list consisting of: viruses, including DNA and RNA viruses, plants, bacteria, pollen and fungi. Even more preferably, the organisms are air pathogens, particularly viruses, preferably the SARS-CoV2 virus.
Thus, the method of the invention is useful for collecting, detecting and identifying air pathogens.
In another preferred embodiment, the method of the invention comprises an additional step (a′), between steps (a) and (b), in which cellular organisms are removed from the device, more preferably from the PTFE filter comprised in the device. Previously to this step (a′), the PTFE filter comprised in the device may be optionally vortex, more preferably at maximum speed for 1 h at 4° C.
The cellular organisms may be removed by, for instance but without limitation, resuspending the airborne particles captured in the filter in saline buffer, followed by centrifugation, shaking or sonication, and finally filtration. Afterwards, a concentration step of the supernatants containing the virus particles may be performed.
Furthermore, preferably, an additional step after step (a′) and before step (b), is carried out, which comprises removing the non-encapsidated DNA or RNA, more preferably with a nuclease treatment.
Methods and uses described in the present invention may be carried out in air samples collected from indoor or outdoor.
Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skilled in the art to which this invention belongs. Methods and materials similar or equivalent to those described herein can be used in the practice of the present invention. Throughout the description and claims the word “comprise” and its variations are not intended to exclude other technical features, additives, components, or steps. Additional objects, advantages and features of the invention will become apparent to those skilled in the art upon examination of the description or may be learned by practice of the invention. The following examples and drawings are provided by way of illustration and are not intended to be limiting of the present invention.
1. Material and Methods.
Sampling
Several sampling devices based on different capturing mechanisms were chosen to compare airborne biological particles (ABPs) capture: three impact/slit samplers (Hirst spore trap sampler (Burkard), Surface Air System DUO 360 (SAS), and Zefon BioPump® Plus (Biopump)), a cyclonic device (Burkard Multivial), a custom impinger and two different filters (Polytetrafluoroethylene (PTFE) and Glass fiber (GFC, 1.7 μm) sandwich with and inner layer of nanoparticles). Hirst spore trap sampler (Burckard) is an impact sampler based on the capture of vacuum-accelerated airborne particles in a vaseline-covered strip. Surface Air System DUO 360 (SAS) was designed for the direct culture of the microorganisms captured from air as is equipped with two heads where agar plates are placed. To reduce the culture bias we replaced the agar plates by vaseline-covered Petri dishes (new plates were used for each sampling day). Zefon BioPump® Plus (Biopump) uses cartridges containing a slide covered by a patented aqueous solution to capture the ABPs which is easier to recover after the sampling (1 cartridge was used per sampling day). Burckard Multivial uses vacuum suction to create a cyclon inside a 1.5 ml tube where ABPs are deposited due to the centrifugal force. A new sterilized 1.5 ml tube was used every day. The custom impinger was built with gas washer bottles (100-200 μm nominal pore size) to capture ABPs by the interchange of particles between the air a buffered solution (MSM buffer: 50 mM Tris-HCl, 100 mM NaCl and 8 mM MgCl2, pH 7.5). For each sampling day a 500 ml bottle of autoclaved buffer were used. Finally, two different filters were used: PTFE (5 μm nominal pore size) and a GFC (1.7 μm, Whatman) sandwich with an inner layer of iron-coated particles (MIL-100(Fe) nanoparticles with 1-10 μm pore size). A GFC-nanoparticle sandwich was prepared directly onto the filter holders. First, a GFC filter was added before injecting an ethanol solution containing a suspension of nanoparticles (˜40 mg). Then, a second GFC filter was added and the sandwiches were dried at 100° C. for 24 h. Filters were reused for the four samplings days. We used duplicates when enough devices were available (Table 1). Sampling was carried out in the roof of the Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid (Spain, 40.439881° N, 3.689409° W, ca 30 m over the street). All samplers were run according to device characteristics (Table 1). Air was sampled during 12 h per day during four consecutive days in May of 2016. Biopump was only run during 10 h due to software limitations, and SAS was only run during 20 min, 3 times per day, to reduce the total volume capture for comparison purpose, since its flow rate is very high (150 L/min) with respect to the other samplers.
1Sampling was repeated during 4 consecutive days.
DNA Extraction
After sampling, total DNA was directly extracted from all devices using PowerMax® Soil DNA Isolation Kit (MO BIO Laboratories), except in the case of impingers that were subjected to tangential flow filtration (70 kDa cartridge) to reduce sample volume from 2 L to ˜10 mL. Vaseline from Burkard and SAS sampler were recovered using a sterile blade and subjected to direct DNA extraction. The aqueous solution of the four Biopump cartridges used, one per day, were recovered and mixed for DNA extraction. ABPs captured by the Burkard Multivial were resuspended in MSM buffer before DNA extraction. Filters (PTFE and GFC) were added directly to DNA extraction tubes. The eluted DNA (5 mL) was then ethanol precipitated. Briefly, 200 μL of 5 M NaCl, 2.5 μL of linear polyacrylamide as carrier (LPA, 25 μg/μL, Sigma) and 10.5 mL of cold absolute ethanol were added. Samples were centrifuged for 30 min at 2500×g. Pellets were washed with cold 70% ethanol and air dried. DNA was resuspended in 100 μl of nuclease free water (Ambion). All procedures were carried out in a UV-cabinet (BioSan UVT-B-AR) and all equipment was treated with 0.1 M HCl solution to avoid contaminations. Two mock DNA extractions were included to test for putative contaminations during extraction. Samples were also tested for the presence of microorganism by PCR using different marked genes (16S rDNA and ITS2) (Table 2). No amplification was observed in mock samples.
Shotgun Sequencing and Analysis
Total DNA samples were randomly amplified using multiple displacement amplification (MDA, GenomiPhi kit, GE Healthcare). 10 μL of each sample were used for amplification following manufacturer's instructions. Samples were amplified for 2.5 h, except for B1 and 11 that required 3.5 h of amplification to obtain sufficient DNA for sequencing. Sample 12 was discarded because no amplification was observed after 6 h. No amplification was observed in mock samples. Library preparations and sequencing were performed at Centro Nacional de Análisis Genómico (CNAG, Barcelona, Spain). Sequencing was done using an Illumina HiSeq 2000 machine obtaining ˜40 M paired-end reads (2×126 pb) for each sample. Raw reads were quality filtered using PRINSEQ (minimum read length 100 pb and minimum average quality 25). Orphan reads were discarded. Taxonomy binning of reads was carried out using Centrifuge against NCBI non-redundant nucleotide database. Only reads uniquely assigned with a score higher than 200 were considered. Reads assigned to Human or PhiX174 were excluded. Centrifuge-assigned reads were normalized using metagenomeSeq and used for beta diversity analysis using PhyloSeq. Quality filtered reads were then assembled with IDBA_UD (--pre_correction --mink 20 --maxk 120 --min_contig 500). Assembled contig with low complexity were removed using PRINSEQ (-lc_method entropy -lc_threshold 70). A hybrid-Blast approach was used for contig taxonomic classification. First, contigs were aligned using Blastn against NCBI non-redundant nucleotide database (NT, downloaded on May 2017). Only those hits with e-value <1e-3 and score >50 were considered, and best hit was assigned. Contigs with no hits or with hits with e-value >1e-3 and score <50 were then subjected to Blastx alignment against NCBI non-redundant protein database (NR, downloaded on May 2017). Again, best hit was used for taxonomic assignments (e-value <1e-3 and score <50). Reads were mapped to contigs using BWA MEM.
Metataxonomic Sequencing and Analysis
In order to obtain a taxonomic profile of the different sampling devices we used a targeted metagenomic approach. MDA-unamplified DNA samples were use as template for marker genes amplification. We used 16S rRNA for bacteria and Internal transcribed spacer 2 (ITS2) for plants and fungi (Table 2 above). PCR amplification and library preparation were carried out at Parque Científico de Madrid (Madrid, Spain). Briefly, 100 pg of DNA, quantified using Picogreen, were used for a first PCR using marker genes primers linked with Illumina adaptors (CS1 and CS2). The PCR conditions were as follow: 98° C. for 30 min, followed by 26 cycles of denaturation at 98° C. for 30 s, 50° C. for 20 s, 72° C. for 20 s, followed by a final extension at 72° C. for 2 min. A second PCR of 8 cycles were performed using a 1/25-1/200 dilution of the first one using the same cycling conditions but using CS1 and CS2 primers linked to different barcodes and additional Illumina adapters also required for sequencing (p5 and p7). Q5® High-Fidelity DNA Polymerase (New England Biolabs) were used for PCRs. Amplified products were quantified and pooled before sequencing in a MiSeq machine obtaining 200,000 reads (2×300pb). Raw reads were quality filtered as described above and paired reads were joined and adapters were removed using PANDAseq. Taxonomic assignments were performed using Qiime software. The Greengenes database (version gg_13_8 implemented in Qiime) was used for bacterias and UNITE (version no. 7.1) was used as fungal database. A custom database was used for plant classification. OTUs were defined at 97% sequence similarity and only those with at least 5 counts and present in at least 2 samples were kept for further analysis. Chloroplast and mitochondrion OTUs were removed from bacterial analysis. Although specific ITS2 primers for plants or fungi were used, some cross-amplification can be produced, and therefore fungal OTUs were removed from plant analysis and plant OTUs from fungal analysis. OTU counts were normalized using the metagenomeSeq method. Taxonomic profile, diversity indexes and beta diversity analysis were performed on normalized counts using Phyloseq package. Common family analysis were performed after merging replicates using Phyloseq. A dedicated Qiime script (differential_abundance.py) was employed to analysis the significance of OTU abundance differences using DESeq2 method.
Virus Sampling, Sequencing and Analysis
For virus analysis we used PTFE filters (1 μm, PALL Zefluor). A vacuum pump equipped with 2 filter holders was placed on Alcobendas city (at 14 km from Escuela Técnica Superior de Ingenieros Industriales, Universidad Politécnica de Madrid) at 1.5 m over the ground. Filters were sampling for 8 days (from the 9 to 17 Feb. 2017) at 2.5 L/min. After sampling, filters were vortexed at maximum speed in 10 mL of MSM buffer for 1 h at 4° C. Cellular organisms were removed by centrifugation (20′ at 3000×g) followed by 0.45 μm filtration of the supernatant. The supernatants containing the virus particles were then concentrated using centrifugal units (100 kDa, Amicon). Concentrated virus particles were subjected to nuclease treatment to remove all non-encapsidated DNA or RNA (200 U of DNAse I, 120 U of Nuclease S7 and 10 μg of RNAse A) for 1 h at RT. Viral DNA was extracted with the MinElute kit (QIAgen), following manufacturer's instructions. Samples were tested for the presence of cellular microorganism by PCR using different marked genes (16S rDNA and ITS2) (Table 2 above) and no amplification was observed neither in the samples nor in the mock sample (10 mL of MSM buffer that were subjected to all steps). Then, 10 μL of each sample were used to randomly amplify all DNA using GenomiPhi kit (GE Healthcare) for 2.5 h. We obtained amplification in both replicates, but not in mock sample. One of the replicates were sequenced at Parque Científico de Madrid using a MiSeq machine, obtaining 682,832 paired reads (2×300 pb). Raw reads were quality filtered using PRINSEQ (minimum read length 150 pb and minimum average quality 25). Paired quality filtered reads were used for assembly using SPAdes v3.9.0. Contigs shorter than 500 pb were discarded. Contigs were aligned using BlastX against the NCBI non-redundant protein database (NR). To remove any putative non-viral sequence, only the contigs with at least 20% of viral hits (e value <1e-3) were considered as viral. Contigs without any hit were also considered as putative viral sequences. Viral contigs were then classified using BlastX against a non-redundant viral protein database (extracted from the NCBI NR database using taxonomic id 10239). Best hits were assigned (e value <1e-3 and score >50). Sequencing reads were mapped against contigs using BWA MEM. Complete circular viral genomes were detected using Minimus2.
Detection of SARS-CoV2 Using PTFE Filters
Five vacuum pumps (KNF) (D1-D5) equipped with 2 filter holder each were installed in La Paz hospital (Madrid, Spain). Two consecutive rounds of sampling were done; from 20/03/2020 to 23/03/2020 (Experiment 1, 3 days) and from 23/03/2020 to 27/03/2020 (Experiment 2, 4 days) (Table 5). Polytetrafluoroethylene (PTFE) filters were used for air sampling at a flow rate of 2.5 l/min. After sampling, filters were immediately immersed in 4 ml of TRIzol (Invitrogen). Three RNA extraction from 1 ml from TRIzol were performed following manufacturer's instructions. For each sample, 3 RNA pellet were resuspended together in 25 μl of Nuclease-Free water (Ambion). For all procedures, DNA Lobind tubes were used (Eppendorf).
SARS-CoV2 E gene was measure using a Taqman assay (Bio-Rad) containing primers and probe designed by Charité Hospital (Berlin) and approved by World Health Organization for clinical diagnosis (Table 3). A 2-step approach was applied. Briefly, 5 μl of RNA was retrotranscribed using the SuperScript IV First-Strand Synthesis System (Invitrogen). Then, 1 μl of cDNA was used as template in a 10 μl qPCR reaction using Taqman Fast Universal PCR Master Mix (Applied Biosystems). Thermal conditions were as follow: 20 seg at 95° C., 45 cycles of 5 seg at 95° C. and 20 seg at 60° C. qPCR was performed in a ABI PRISM 7900HT SDS device (Applied Biosystems). Samples were evaluated using technical triplicates.
ORF1ab and N genes were measure in a one-step approach using the Novel Coronavirus (2019-nCoV) Nucleic Acid Diagnostic Kit (Sansure). Briefly, 2.5 μl and 5 μl of RNA from Experiments 1 and 2 respectively, were used in a 25 μl qPCR reaction. Thermal conditions were as follow: 30 min at 50° C. for retrotranscription, 1 minute at 95° C. followed by 45 cycles of 15 seg at 95° C. and 30 seg at 60° C. One step qPCR was performed in a CFX-384 device (Bio-Rad).
2. Results.
Shotgun Sequencing Approach
To obtain a global view of the airborne biological community without the restriction of targeted metagenomic approaches, that do not include viruses, we decided to sequence total DNA using a shotgun sequencing approach. However, the amount of total DNA recovered from the air samples was <1 ng/μl, and therefore we had to randomly amplify the DNA samples using Multiple Displacement Amplification (MDA) to obtain sufficient DNA for library preparation. All samples were amplified for 2.5 h, except by Burkard 1 (B1) and Impinger 1 (I1) that required 3.5 h of amplification to obtain sufficient DNA. The Impinger 2 (I2) sample was discarded because no DNA amplification was observed even after 6 h of MDA. Total DNA was directly sequenced using the Illumina technology, obtaining ˜40 million paired reads for each sample. Raw reads were subjected to quality filtering prior to contig assembly. We obtained on average 13,000 contigs per sample, being the impinger (I1) the sample with fewer contigs, closely followed by the Biopump (BP) and one of the Burkard replicates (B1). By contrast, SAS, Burkard Multival (BM) and the other Burkard replicate (B2) showed the highest number of contigs. Total number of assembled bases was ˜18 million on average, but one of the Burkard samples (B1), the Biopump (BP), one of the GFC filters (N1) and the impinger (I1) were clearly under this average which correlated with a reduced number of contigs. However, average contig length and N50 were similar among all samples except for I1 that was almost twice with respect to all other samplers.
Contigs were classified using both Blastn and Blastx against the NCBI non-redundant databases (
Although the results of these shotgun experiments are dominated by plant sequencing reads, mainly from Pinus genus, we were able to detect some viral contigs (Table 4).
Most of them were classified as Baculoviridae and Caulimoviridae, insect and plant viruses respectively. We were also able to detect some bacteriophage (Caudovirales) contigs in sample 11, which correlates with a bacterial contamination in that sample, although some of them could represent prophages rather than free virus. Among viral contigs we were able to detect 5 complete circular viral genomes: one Circoviridae-like contig detected in B1, one Genomoviridae-like virus detected in S1 and three Caulimoviridae-like virus detected in B2, BM and S1. Another near-complete Caulimoviridae-like virus was also detected in S2 sample, and many caulimo-related contigs were also detected in other samples. Moreover, using the Caulimoviridae-like virus detected in B2 (contig B2_191) as reference we were able to detect reads from this virus in almost all samples except in 11. Samples B1 (Burkard) and BP (BioPump) showed very few Caulimoviridae-like reads compared to the other samples. These Caulimoviridae-like viruses have been demonstrated to infect Pinus and could represent the first gymnosperm-infecting Caulimovirus described to date.
Metataxonomic Approach (Targeted Metagenomics)
Due to the Viridiplantae dominance in shotgun sequencing and the impossibility of doing a convenient comparative analysis, we decided to use the unamplified DNA samples to amplify marker genes to obtain a taxonomic profile of the microorganisms captured by the different sampling devices. We used 16S rRNA for bacteria and ITS2 for plants and fungi. Amplicons were sequenced in a MiSeq device obtaining ˜200,000 paired sequencing reads (2×300 pb) from each sample. Using this approach, we were able to amplify 16 rRNA from both impinger samples, however we did not obtain amplification of ITS2 (either from fungi or plants) from these two samples neither using a higher number of PCR cycles (data not shown). This result was consistent with the bacterial contamination observed in the shotgun analysis of these samples.
Bacteria Analysis
As mentioned above, Impingers taxonomic profile were mostly composed by Rhodobacterales from Paracoccus genus arising up to ˜95% of the reads in sample 11 (
Regarding the captured diversity, Burkard (B), SAS (S) and PTFE (T) showed the highest value in almost all indexes (
Fungi Analysis
The ITS2 region was amplified and sequenced for fungi taxonomic analysis. A general dominance of the order Capnodiales, most of them from Cladosporium genus, was observed in all samples (
However, Burkard, together with SAS and PTFE, showed high values in most diversity indexes (
Plants Analysis
Plants were mainly capture in the samplers through pollen grain or small fragments present in the air. In general, the results of the analysis from plants showed a similar behavior than in bacterial and fungal analysis (
Virome Analysis
PTFE and SAS showed the best efficiencies capturing microbial diversity from the air (
Detection of SARS-CoV2
For experiment 1 and 2, default setting were applied for the analysis. Only cycle threshold (Ct) below 40 with “S” shape were considered as valid. No template controls (NTC) and positive controls were included in all runs. In the table below, Ct for all three genes (E, ORF-1ab, N) in both experiments are shown in table 5.
3. Conclusions.
Here we have presented a comparative analysis of different air samplers. Our first choice was a shotgun approach to obtain a global view of all organisms present in the air. In our experimental setting, plants seemed to dominate regardless of the sampling method used (
It is interesting to identify the differences in the plant taxonomic profile detected using metataxonomic and shotgun approaches. Fagales were the most abundant taxa in the ITS2 profile (˜50% on average), while Pinales dominated shotgun reads (˜80%,
Nevertheless, using a targeted metagenomic approach we were able to compare different samplers avoiding the dominance of sequencing reads from plant genomes observed by shotgun analysis. In our analysis of the outdoor air, samplers had a low relative influence on the capture of biodiversity, showing most of them a similar taxonomic profile, although some important differences were observed (
Apart from the cost, one of the major challenges for study airborne microorganisms is the amount of biomass and therefore the amount of DNA that can be obtained. This could be partially solved by the used of random amplification methods such as MDA or Sequence-Independent Single-Primer Amplification (SISPA). However, as shown here, when a shotgun approach is used, it is important to consider the presence of pollen that can dominate most of the reads, although most of them could not be classified due to database deficiencies. In this sense, targeted metagenomics could be a good solution. However, viruses cannot be studied following this targeted approach. Viruses do not have any common marker gene to study them, and only a shotgun approach can be used. Using such approach, in spite of the dominance of plant reads, we were able to detect viral contigs, being some of them complete genomes. Moreover, we were able to detect and describe a new viral genome (Pinus nigra virus 1) belonging to a new putative Caulimoviridae genus infecting gymnosperms. By contrast, the circo-like contig detected in B1 sample that was 99% identical to MG023129.1, a viral genome detected on marine isopods, could represent a contamination of the silica used in the DNA extraction kit columns as it was previously reported.
Additionally, viruses can have DNA or RNA genomes and analysing only DNA will result in a biased view of viral diversity. Moreover, most human infecting viruses are RNA viruses such as Influenza or Enterovirus (Rhinovirus). Therefore, for environments with very different organisms and a variety of genome lengths, the best option to study viruses is the purification of virus particles before sequencing. However, this is not an easy task for most samplers. For example, SAS and Burkard use vaseline layers to capture the airborne particles and the purification of viruses or cells from this substance, by using chloroform or other organic solvent, can destroy most of cellular organisms and some viruses. As we show here, PTFE filters represent the best option for viral metagenomics because of the easy to extract cellular organism and virus particles by shaking or sonication of the filters in a buffer.
In conclusion, we have tested several sampling devices, using different capturing mechanisms, for the analysis of the airborne biological community in order to establish a standardized method. First, we tried using a shotgun sequencing approach, a method that would allow the sequencing of all microorganisms present in the samples. However, we observed that this approach is not the most convenient when the community is composed by organisms with very different genomes sizes. In our experiments, pollen grains from Pinus, which have a very large genome (22 Gb), have monopolized most of the sequencing reads and only a small fraction of the reads belonged to other taxonomic groups. A deeper sequencing could solve partially this problem, although the sequencing cost could also make the use of this approach prohibitive. Therefore, community diversity should be considered before using a shotgun sequencing approach. By contrast, amplicon sequencing, a simpler and cheaper method, allowed us to compare the communities captured by the different sampling devices, despite the genome size diversity. Using this approach, we showed that PTFE filters and SAS are the most suitable samplers for the analysis of bacteria, fungi spores and pollen from plants, with very little differences between them. Other samplers, such as Burkard, also showed a good performance, but the consistency between replicates was poor compared to SAS and PTFE, which is crucial in comparative studies. Additionally, taking into account other factors such as cost and portability, PTFE filters were the most convenient device. Finally, we have demonstrated that PTFE filters allow the extraction of the viral fraction for viral metagenomics, which allows the analysis of the whole airborne biological community.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20382510.4 | Jun 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/065932 | 6/14/2021 | WO |
