Patent Application
20210084905
Acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) is an emerging epizootic disease that impacts Litopenaeus vannamei shrimp. The causative agent is Vibrio bacteria that harbor a plasmid that encodes a secreted binary toxin (PirAB) that possesses structural similarity to other known insecticidal toxins. The current disease model proposes V. parahaemolyticus strains that carry this vector colonize shrimp and then secrete toxin molecules causing necrosis of the shrimp hepatopancreatic tissue thus leading to mortality. Because V. parahaemolyticus is prevalent and ubiquitous in warm seawater and brackish estuaries and also found to colonize crustaceans and other invertebrates, it has been nearly impossible to completely protect large scale aquaculture from AHPNS strains where shrimp are farmed. AHPNS was first identified in China in 2009 and spread to Malaysia, Vietnam, Thailand, and the Philippines through 2013 and remains a problem. In 2017 it was also detected in shrimp aquaculture in Latin America. The Global Aquaculture Alliance (GAA) estimated losses caused by EMS disease to exceed one billion dollars per year. Thus, there is a need for novel and innovative treatments for AHPNS in aquaculture.
Provided herein are compositions and methods of preventing or treating acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) in cultured (e.g., farmed) crustaceans (e.g., shrimp or prawns).
The methods provided herein comprise methods of inhibiting the growth of pathogenic bacteria in cultured crustaceans by administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. The pathogenic bacteria may be Vibrio bacteria (e.g., V. cholera, V. vulnificus, V. harveyi, V. cholerae, V. aliginolyticus. A. hydrophila, or A. media). The Vibrio bacteria may be V. parahaemolyticus. The pathogenic bacteria may be an Aeromonas pathogenic bacteria (i.e., not Aeromonas hydrophila A603), such as A. hydrophila, A. caviae, A. sobria, or A. media. The bacteria may be antibiotic resistant. The pathogenic bacteria may be any pathogenic bacteria, including, but not limited to, the bacteria disclosed herein or any bacteria found in or on the bodies of shrimp. The pathogenic bacteria may be associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). The pathogenic bacteria may not associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS).
Also provided herein are methods of treating or preventing bacterial infection in cultured crustaceans by administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. The bacterial infection may be caused by Vibrio bacteria (e.g., V. cholera, V. vulnificus, V. harveyi, V. cholerae, V. aliginolyticus. A. hydrophila, V. parahaemolyticus or A. media). The bacterial infection may be caused by an Aeromonas pathogenic bacteria (i.e, not Aeromonas hydrophila A603) such as A. hydrophila, A. caviae, A. sobria, or A. media. The bacterial infection is caused by pathogenic bacteria that are antibiotic resistant. The bacterial infection may be caused by any pathogenic bacteria, including, but not limited to, the pathogenic bacteria disclosed herein or any bacteria found in or on the bodies of shrimp. In some embodiments, the pathogenic bacteria causing the bacterial infection is associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In other embodiments, the pathogenic bacteria causing the bacterial infection is not associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In some aspects, provided herein are methods of overcoming or inhibiting antibiotic resistance in cultured crustaceans comprising administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans.
The methods include treating or preventing bacterial (e.g., Vibrio bacteria) infection in cultured crustaceans by administering the Aeromonas hydrophila A603 bacteria to the environmental waters comprising the cultured crustaceans. In some aspects, provided herein are methods of inhibiting the growth of Vibrio bacteria in cultured crustaceans comprising administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. In some aspects, provided herein are methods of treating or preventing acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) in cultured crustaceans comprising administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. In some embodiments, the crustaceans are in a larval stage. In some embodiments, the crustaceans are mature crustaceans. The cultured crustaceans may be shrimp (e.g., Litopenaeus vannamei shrimp). In some embodiments, the environmental waters have tested positive for Vibrio bacteria or any bacteria causing acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In some embodiments, the environmental waters have tested positive for Vibrio bacteria, and the Vibrio bacteria are antibiotic resistant. The Vibrio bacteria may be V. cholera or V. parahaemolyticus (e.g., EMS V. parahaemolyticus). The environmental waters may be seawater or brackish water. In some embodiments, the Vibrio bacteria is associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In other embodiments, the Vibrio bacteria is not associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS).
In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent that increases the expression of T6SS proteins. In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent that increases the expression of T6SS proteins prior to administering the Aeromonas hydrophila A603 bacteria to the environmental waters comprising the cultured crustaceans. In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent that increases the expression of T6SS proteins by administering the Aeromonas hydrophila A603 bacteria and the agent to the environmental waters comprising the cultured crustaceans. The agent may be an expression vector. In some embodiments, the expression vector encodes for a T6SS effector protein or a T6SS machinery protein (e.g., a protein that aids in or is part of T6SS assembly).
In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent that activates phenazine biosynthesis. In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent that activates phenazine biosynthesis prior to administering the Aeromonas hydrophila A603 bacteria to the environmental waters comprising the cultured crustaceans. The agent may be an expression vector. In some embodiments, the expression vector comprises a gene or a portion of a gene in the phenazine operon. The agent may be an acylated homoserine lactone (AHL) molecule or a PhzR protein.
In some embodiments, the method further comprises administering the Aeromonas hydrophila A603 bacteria to the environmental waters comprising the cultured crustaceans conjointly with a phenazine (e.g., pyocyanin), a phenazine precursor, or phenazine derivative.
In some aspects, provided herein are methods of treating a bacterial growth or infection (e.g., a bacterial growth or infection described herein) by administering phenazine (e.g., pyocyanin), a phenazine precursor, or phenazine derivative to the environmental waters comprising the cultured crustaceans. In some embodiments, the methods comprise administering phenazine (e.g., pyocyanin), a phenazine precursor, or phenazine derivative to the environmental waters comprising the cultured crustaceans.
In some embodiments, the Aeromonas hydrophila A603 is administered to the environmental waters comprising the cultured crustaceans conjointly with an antibiotic. The antibiotic may be administered to the environmental waters comprising the cultured crustaceans prior to Aeromonas hydrophila A603 administration. The antibiotic (e.g., an antibiotic that does not target Aeromonas hydrophila A603) may be administered to the environmental waters comprising the cultured crustaceans simultaneous to Aeromonas hydrophila A603 administration.
Provided herein are compositions comprising Aeromonas hydrophila A603. The composition may be a probiotic. The composition may be feed used for industrial crustaceans farming or aquaculture. The compositions disclosed herein may comprise a phenazine (e.g., pyocyanin). The composition may comprise any agent that increases phenazine biosynthesis (e.g., an AHL molecule or a PhzR protein). In some embodiments, the composition comprises a T6SS effector protein. The composition may further comprise and antibiotic (e.g., an antibiotic that does not target Aeromonas hydrophila A603).
Provided herein are methods and compositions of aquaculture. Such methods include preventing or treating acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) in cultured crustaceans (e.g., shrimp or prawns). The methods include treating or preventing bacterial (e.g., Vibrio bacteria) infection in cultured crustaceans by administering Aeromonas A603 bacteria to the environmental waters comprising the cultured crustaceans.
For convenience, certain terms employed in the specification, examples, and appended claims are collected here.
As used herein, the term “administering” means providing an agent or composition to the environmental waters comprising crustaceans described herein. “Administering” may include any other means of providing the crustaceans described herein with the compositions described herein.
The term “agent” is used herein to denote a chemical compound, a small molecule, a mixture of chemical compounds and/or a biological macromolecule (such as a small molecule or a protein or a peptide). The activity of such agents may render them suitable as a “agent” which is a biologically, physiologically, or pharmacologically active substance (or substances) that acts locally or systemically.
The term “amino acid” is intended to embrace all molecules, whether natural or synthetic, which include both an amino functionality and an acid functionality and capable of being included in a polymer of naturally-occurring amino acids. Exemplary amino acids include naturally-occurring amino acids; analogs, derivatives and congeners thereof; amino acid analogs having variant side chains; and all stereoisomers of any of the foregoing.
The term “peptide” refers to a polypeptide, in certain embodiments prepared from recombinant DNA or RNA, or of synthetic origin, or some combination thereof, which (1) is not associated with proteins that it is normally found with in nature, (2) is isolated from the cell in which it normally occurs, (3) is isolated free of other proteins from the same cellular source, (4) is expressed by a cell from a different species, or (5) does not occur in nature.
The terms “polynucleotide” and “nucleic acid” are used interchangeably. They refer to a polymeric form of nucleotides of any length, either deoxyribonucleotides or ribonucleotides, or analogs thereof. Polynucleotides may have any three-dimensional structure, and may perform any function, known or unknown. The following are non-limiting examples of polynucleotides: coding or non-coding regions of a gene or gene fragment, loci (locus) defined from linkage analysis, exons, introns, messenger RNA (mRNA), transfer RNA, ribosomal RNA, ribozymes, cDNA, recombinant polynucleotides, branched polynucleotides, plasmids, vectors, isolated DNA of any sequence, isolated RNA of any sequence, nucleic acid probes, and primers. A polynucleotide may comprise modified nucleotides, such as methylated nucleotides and nucleotide analogs. If present, modifications to the nucleotide structure may be imparted before or after assembly of the polymer. The sequence of nucleotides may be interrupted by non-nucleotide components. A polynucleotide may be further modified, such as by conjugation with a labeling component. The term “recombinant” polynucleotide means a polynucleotide of genomic, cDNA, semisynthetic, or synthetic origin which either does not occur in nature or is linked to another polynucleotide in a non-natural arrangement.
As used herein, the term “subject” means a non-human animal selected for treatment or therapy, such as shrimp. The term “shrimp” includes decapod crustaceans. Used broadly, it may cover any of the groups with elongated bodies and a primarily swimming mode of locomotion, such groups include Caridea and Dendrobranchiata.
“Treating” a disease in a subject or “treating” a subject having a disease refers to subjecting the subject to a pharmaceutical treatment, e.g., the administration of a drug, such that at least one symptom of the disease is decreased or prevented from worsening.
Provided herein are methods of preventing or treating acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) in cultured crustaceans (e.g., shrimp or prawns). Provided herein are methods of treating or preventing pathogenic bacterial (e.g., Vibrio bacteria or pathogenic Aeromonas bacteria, not including Aeromonas hydrophila A603 bacteria) infection or inhibiting pathogenic bacterial growth by administering Aeromonas hydrophila A603 bacteria or compositions comprising Aeromonas hydrophila A603 bacteria to the environmental waters comprising the cultured crustaceans. The methods provided herein comprise methods of inhibiting the growth of pathogenic bacteria in cultured crustaceans by administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. The pathogenic bacteria may be any species of Vibrio bacteria (e.g., V. cholera, V. vulnificus, V. harveyi, V. cholerae, V. aliginolyticus. A. hydrophila, or A. media). The Vibrio bacteria may be V. parahaemolyticus. The pathogenic bacteria may be an Aeromonas pathogenic bacteria (i.e., not Aeromonas hydrophila A603), such A. hydrophila or A. media. The bacteria may be antibiotic resistant. The pathogenic bacteria may be any pathogenic bacteria, including, but not limited to, the bacteria disclosed herein or any bacteria found in or on the bodies of shrimp. The pathogenic bacteria may be associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). The pathogenic bacteria may not associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS).
Also provided herein are methods of treating or preventing bacterial infection in cultured crustaceans by administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans. The bacterial infection may be caused by Vibrio bacteria (e.g., V. cholera, V. vulnificus, V. harveyi, V. cholerae, V. aliginolyticus. A. hydrophila, V. parahaemolyticus or A. media). The bacterial infection may be caused by an Aeromonas pathogenic bacteria (i.e, not Aeromonas hydrophila A603) such as A. hydrophila or A. media. The bacterial infection is caused by pathogenic bacteria that are antibiotic resistant. The bacterial infection may be caused by any pathogenic bacteria, including, but not limited to, the pathogenic bacteria disclosed herein or any bacteria found in or on the bodies of shrimp. In some embodiments, the pathogenic bacteria causing the bacterial infection is associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In other embodiments, the pathogenic bacteria causing the bacterial infection is not associated with acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In some aspects, provided herein are methods of overcoming or inhibiting antibiotic resistance in cultured crustaceans comprising administering Aeromonas hydrophila A603 bacteria to environmental waters comprising the cultured crustaceans.
The crustaceans described herein may be any crustacean cultured in industrial aquaculture. Examples of such crustaceans, include, but are not limited to, shrimp of the family Penaeidae, such as Litopenaeus vannamei (Pacific white shrimp) and Penaeus monodon (giant tiger prawn). Administering Aeromonas hydrophila A603 bacteria or the compositions described herein may be administered at any point in the crustaceans life cycle, including egg, larval, nauplii, mysis, postlarvae, and/or mature (adult) stages. In some embodiments, the crustaceans are mature crustaceans. In some embodiments, the environmental waters have tested positive for Vibrio bacteria and/or any bacteria causing acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS). In some embodiments, the environmental waters have tested positive for Vibrio bacteria, and the Vibrio bacteria are antibiotic resistant. The Vibrio bacteria may be V. cholera or V. parahaemolyticus (e.g., EMS V. parahaemolyticus). In some embodiments, the Vibrio bacteria may be a Ta Mai strain of Vibrio bacteria. Environmental waters, as described herein, may be any body of water comprising crustaceans. The environmental waters may be seawater, brackish water, or the water may comprise freshwater.
In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent (e.g., a nucleic acid vector) that increases the expression of type VI secretion system (T6SS) proteins. The T6SS is molecular machine used by a wide range of gram-negative bacterial species to transport proteins from the interior (cytoplasm or cytosol) of a bacterial cell across the cellular envelope into an adjacent target cell. The T6SS consists of proteins that assemble into three sub-complexes: a phage tail-like tubule, a phage baseplate-like structure, and cell-envelope spanning membrane complex. These three subcomplexes work together to transport proteins across the bacterial cell envelope and into a target cell through a contractile mechanism. In some embodiments, the expression vector encodes proteins involved in T6SS machinery or assembly, such as proteins that assemble the phage tail-like tubule, a phage baseplate-like structure, and/or the cell-envelope spanning membrane complex. In some embodiments, the expression vector may encode for T6SS effector proteins, such as toxic proteins delivered by T6SS machinery to the target bacteria. Examples of T6SS effector proteins include, but are not limited to, proteins encoded by tseA, tseB, and tseC (e.g., TseA, TseB, and TseC). T6SS effector proteins may include any T6SS effector protein that are antibacterial by function.
Provided herein are nucleic acid molecules or polynucleotides that encode the T6SS proteins described herein. For example, the polynucleotide may encode a T6SS protein or fragment thereof. The nucleic acids may be present, for example, in whole cells, in a cell lysate, or in a partially purified or substantially pure form.
Nucleic acids described herein can be obtained using standard molecular biology techniques. For example, nucleic acid molecules described herein can be cloned using standard PCR techniques or chemically synthesized.
In certain embodiments, provided herein are vectors that contain the isolated nucleic acid molecules described herein (e.g., a T6SS protein). As used herein, the term “vector,” refers to a nucleic acid molecule capable of transporting another nucleic acid to which it has been linked. One type of vector is a “plasmid”, which refers to a circular double stranded DNA loop into which additional DNA segments may be ligated. Another type of vector is a viral vector, wherein additional DNA segments may be ligated into the viral genome. Certain vectors are capable of autonomous replication in a host cell into which they are introduced (e.g., bacterial vectors having a bacterial origin of replication and episomal mammalian vectors). Other vectors (e.g., non-episomal mammalian vectors) can be integrated into the genome of a host cell upon introduction into the host cell, and thereby be replicated along with the host genome. Moreover, certain vectors are capable of directing the expression of genes. Such vectors are referred to herein as “recombinant expression vectors” (or simply, “expression vectors”).
In some embodiments, the method further comprises contacting the Aeromonas hydrophila A603 bacteria with an agent (e.g., a nucleic acid vector, a peptide, or a small molecule) that activates phenazine biosynthetic pathway. The agent may be an acylated homoserine lactone (AHL) or a PhzR protein. The agent may be an expression vector. In some embodiments, the expression vector may comprise a gene or part of a gene in the phenazine biosynthetic operon. Examples of such genes include, but are not limited to, genes listed in
Antibiotics are commonly used in shrimp farming to prevent or treat disease outbreaks. In some embodiments, Aeromonas hydrophila A603 bacteria is administered to the environmental water comprising the cultured crustaceans conjointly with one or more antibiotics. The antibiotic may be administered to the environmental waters comprising the cultured crustaceans prior to Aeromonas hydrophila A603 administration, in order to substantially eliminate existing bacteria in the cultured crustaceans and/or the environmental waters. For example, antibiotics may be administered to the environmental waters, and, after a period of time, Aeromonas hydrophila A603 is administered to the environmental waters. A period of time may be at least an hour, at least 24 hours, at least 48 hours, at least one week, at least two weeks, or at least a month. The one or more antibiotics may be selected from oxytetracycline, florfenicol, sarafloxacin, enrofloxacin, chlortetracycline, quinolones, ciprofloxacin, norfloxacin, oxolinic acid, perfloxacin, sulfamethazine, gentamicin, and/or tiamulin. The antibiotic (e.g., an antibiotic that does not target Aeromonas hydrophila A603) may be administered to the environmental waters comprising the cultured crustaceans simultaneously to Aeromonas hydrophila A603 administration. Aeromonas hydrophila A603 may be antibiotic resistant. The antibiotic (e.g., streptomycin) may be administered to the environmental waters comprising the cultured crustaceans simultaneously to antibiotic resistant (e.g., streptomycin-resistant) Aeromonas hydrophila A603 administration. In certain embodiments, agents of the invention may be used alone or conjointly administered with another type of therapeutic agent (e.g., an antibiotic). As used herein, the phrase “conjoint administration” refers to any form of administration of two or more different therapeutic agents/bacteria such that the second agent is administered while the previously administered therapeutic agent is still effective in the body or environmental waters (e.g., the two agents are simultaneously effective in the subject, which may include synergistic effects of the two agents). For example, the different therapeutic agents/bacteria can be administered either in the same formulation or in separate formulations, either concomitantly or sequentially.
Aeromonas hydrophila A603 may be administered at any concentration or dosage needed to inhibit pathological bacteria (e.g., Vibrio bacteria) growth or treat or prevent bacterial infection. Aeromonas hydrophila A603 may be measured in colony forming units (cfu). Aeromonas hydrophila A603 may be administered in approximately equal, less, or more colony forming units as the estimated amount of pathological bacteria in the environmental waters. For example, at least 1 million, at least 100 million, at least 500 million, at least 1 billion, at least 100 billion, at least 500 billion, at least 1 trillion, at least 100 trillion, at least 500 trillion, at least 1 quadrillion, at least 100 quadrillion, or at least 500 quadrillion may be administered to the environmental waters comprising the cultured crustaceans.
Provided herein are compositions that comprise Aeromonas hydrophila A603 for the treatment or prevention of acute hepatopancreatic necrosis syndrome (AHPNS) or early mortality syndrome (EMS) in cultured crustaceans (e.g., shrimp or prawns). In some embodiments, the composition is a probiotic. Compositions disclosed herein may be used as a feed additive or supplement in crustacean farming techniques. For example, the compositions disclosed herein may be added to processed fish meal prior to feeding crustaceans in aquaculture. The feed maybe a dry feed. The feed may be a micro-encapsulated feed. The feed may be entrapped in a liposome and the liposome is further encapsulated in a hydrocolloid matrix. The feed may be in the form of complex microcapsules (CXMs) consisting of dietary ingredients and lipid-wall microcapsules (LWMs) embedded in particles of a gelled mixture of alginate and gelatin to obtain a single food-particle type used to provide suspension feeders with dietary nutrients. The feed may be a liquid food stuff. Liquid foodstuff may include particulate feed in a liquid medium and provides an easy convenient way to deliver a nutritionally formulated ration to crustaceans. The liquid foodstuff may include oil-coated nutrient feed particles which are embedded in a gel or a food in a polymer blend. The gel may be crosslinked or complexed to encapsulate the oil-coated nutrient to provide encapsulated oil-coated nutrient feed. The particulate feed may be adjusted for the requirements of the marine animal being fed. The feed may comprise animal protein, brine shrimp, egg product, betaine, alanine, isoleucine, leucine, serine, valine, glycine, astaxanthin, vitamin A supplement, vitamin B 12 supplement, riboflavin supplement, calcium pantothenate, niacin supplement, vitamin D 3 supplement, vitamin E supplement, menadione sodium bisulfite complex, folic acid, biotin, thiamine, pyridoxine hydrochloride, inositol and/or choline chloride.
In some embodiments, the composition further comprises a phenazine. In some embodiments, the composition further comprises an activator of the phenazine biosynthetic pathway (e.g., AHL or a PhzR protein). In some embodiments, the composition further comprises an antibiotic. The antibiotic may be oxytetracycline, florfenicol, sarafloxacin, enrofloxacin, chlortetracycline, quinolones, ciprofloxacin, norfloxacin, oxolinic acid, perfloxacin, sulfamethazine, gentamicin, or tiamulin. In some embodiments, the composition further comprises a phenazine, a phenazine precursor, a phenazine derivative, a phenazine based molecule, or any other intermediate molecule in the phenazine biosynthetic pathway. The phenazine may be pyocyanin. Examples of phenazine precursors, derivatives, or intermediates may be found in
Strains isolated from infected shrimp that also carry the genes for the toxin on a plasmid are not always clonal or closely related suggesting the transmission of this plasmid among environmental Vibrio parahaemolyticus strains is sufficient to create a diverse assemblage of pathogenic strains and that the disease may be solely attributed to this vector (
An Aeromonad with antibacterial activity against bacteria of the genus Vibrio was identified in a screen using a panel of bacterial isolates from shrimp imported from China (
When approximately 100 million Vibrio are incubated with Aeromonas A603 for two hours and plated on selective media the result is that fewer than 100 colony forming units (cfu) of Vibrio can be recovered (
The genome of A603 was sequenced using both Illumina and Pacific Biosciences next generation sequencing platforms yielding a closed and complete 4.8-Megabase genome. Using the genome and predicted genes it was possible to identify potential antibacterial components in A603 by looking for the Type VI secretion system (T6SS), antimicrobial metabolic pathways, bacteriocins, and bacteriophages. In addition to a Mu phage, a T6SS genomic core island and a separate accessory T6SS island (Island II) are found in A603 and these resemble genetic operons found in other Aeromonas strains (
When the T6SS machinery is assembled, it targets other cells through a contact-dependent mechanism by contracting and then ejecting effector proteins across its membrane and into another “prey” cell (
To examine the role and contribution of the T6SS in A603 antibacterial activity, a gene that encodes a T6SS structural protein essential for activity was precisely deleted (
A603 inhibits the growth of a variety of bacterial strains seeded into an agar soft overlay by secretion of an antibacterial compound independent of the vipA gene (
The spectrum of inhibition for the putative phenazine molecule was tested by seeding agar with a diverse set of laboratory and environmental strains using A603 ΔvipA and an isogenic double knockout A603 ΔvipA Δorf8 to score inhibition by appearance of a halo around A603 ΔvipA. Unlike T6SS, which is only known to target a subset of gram-negative bacteria, this secreted molecule inhibits the growth of a broad range of both gram negative and gram positive strains (
Both the T6SS and the phenazine-based molecule are shown to act independently as antimicrobial mechanisms when tested on Vibrio strains. A panel of A603 strains lacking either and both vipA and orf8 were incubated with Vibrio strains to measure the contribution of each antibacterial mechanism. When co-incubated with various Vibrio and Aeromonas strains, the sensitivity to each mechanism appears to vary in a bacteria-dependent manner and the A603 ΔvipA Δorf8 strain has no measurable antibacterial activity. For EMS strains, T6SS is the most significant killing mechanism within one hour as it's killing activity is ˜500× that of the phenazine (
Synergistic cooperativity is not apparent or detected within the resolution of this assay however genetic elements within one T6SS cluster and the phenazine biosynthetic pathway suggest some co-regulation or crosstalk. The T6SS cluster II (
Some of the accessory or hypothetical genes in the phenazine operon are predicted to have functions critical to phenazine or shikimic acid synthesis while other genes present in the A603 genome appear unique and are not identified in other phenazine operons (
To test the antibiotic activity and a putative role in probiotic protection, shrimp (Litopenaeus vannamei) were incubated with Aeromonas A603 and EMS Vibrio parahaemolyticus strains to measure the colonization of each strain and whether A603 could antagonize colonization of EMS strains in vivo. This was done by adding 5×105/ml cfu of either or both strains to 500 ml seawater using 1-2 gram shrimp and then measuring bacteria in both water and shrimp over 48 hours. Bacterial abundance was measured using Illumina sequenced DNA obtained from bacteria isolated from 1 ml of water and from the filtrate of a homogenized shrimp. Upon DNA extraction, a quantified DNA standard for a ˜1000 bp nonbacterial artificial gene produced by PCR was also added to each sample before Illumina libraries were built and amplified in order to normalize reads as bacterial abundance could bias distributions of each strain. After Illumina sequencing, reads were mapped to the standard and also the A603 and EMS reference genomes including the pVPA3 PirA/B plasmid and the measure of each strain was calculated (
Shrimp uninfected with EMS (24 hours+/−A603, A1/A2 & B1/B2) were found to have an apparent low level of colonization of EMS Vibrio (10-100 per shrimp) prior to infection with Ta Mai strain, but this is likely due to present environmental Vibrio that share some genome sequence homology with the EMS strains. Shrimp infected with only the Ta Mai strain were measured to have between 10,000 and 100,000 cfu per shrimp (A3 &A4) and those pretreated with A603 were measured to have 100-1000× fold fewer Ta Mai strain (B3 & B4). The colonization of shrimp by A603 was measured to be low, between 10-100 per shrimp or per 1 ml water.
The sequence data for each sample was utilized for additional analysis of the complete microbiome using MG-RAST pipeline (
The transcriptomes of both A603 and Ta Mai strains were analyzed in order to determine interbacterial antagonism and induced responses in both bacteria when co-cultured. The A603 transcriptome was not impacted significantly within its ˜4300 genes except for a handful of genes within a few operons. All three tetrathionate reducate subunit genes (ttrABC) are upregulated 100-500 fold. These encode a membrane bound complex that reduces tetrathionate to thiosulfate. Concomitantly, a separate operon that encodes a lactate permease and utilization contains the four most downregulated genes (˜20-fold). In Citrobacter freundi, lactate was shown to be a poor electron donor to tetrathionate reduction which may explain this strategy. The dynamic resolution provided in this analyses captures other subtle transcriptional responses likely due to the availability of oxygen, metabolites, or other resources in the co-culture but no indication of stress-related pathways are apparent. This is supported by the absence of killing by A603 Δorf8 ΔvipA by all tested Vibrio species, including a well-characterized V. cholerae isolate with an active T6SS that is significantly bactericidal to many gammaproteobacteria.
In A603, the most highly expressed gene encodes a 71 amino acid protein that is nearly identical to the H. pylori HP 1242 protein. The solved structure of this small protein is composed of three (3-helices and folds in a coiled-coil-like conformation. Both proteins possess a domain of unknown function (DUF465 family) and though this is the most abundantly expressed transcript in this strain, its role is unclear. The remaining four most highly expressed genes encode other proteins, some found to be highly expressed in other gram negative bacteria; these include a S1-like cold shock domain protein, an acyl carrier protein, a FimA-like pilin, and a porin/adhesion. Expanding this list to include the highest 2% of expressed A603 genes in both mono- and co-cultures, it was found that the majority have roles in translation, arginine dihydrolase, ATP synthesis, and other key genes that share common function are related to T6SS or phenazine biosynthesis.
Because AHPNS strains are killed within 120 minutes by A603, the transcriptomes were measured 45 minutes post-incubation to capture responses prior to cell death. In contrast to A603, the Ta Mai transcriptome is significantly altered when co-cultured and the most significantly up-regulated genes are correlated to stress, oxidative damage, and DNA repair. The genes upregulated and downregulated more than 3-fold were extracted and their corresponding GO annotations and abundance were used to extract enrichment of biological processes and pathways using hypergeometric tests. All genes with measured expression were also analyzed using Gene Set Enrichment Analysis (GSEA). Both analyses identified the same A603-induced cell stress pathways in Ta Mai including the DNA repair, SOS response, and oxidation-reduction. These processes were significantly induced when co-cultured with A603 strains operative for T6SS and phenazine molecule biosynthesis. Curiously, pathogenesis was also identified as a significant process as genes that encode Type III secretion and the PirAB toxin components are significantly induced. These genes would normally be induced during infection in a host and may reflect a response initiated by stress mimetic to that of an immune response. A spermidine transmembrane transporter activity is also identified as a key process and the only pathway deemed significant in all co-incubations with A603, regardless of T6SS and the phenazine molecule. The arginine hydrolase pathway is ubiquitously highly expressed in A603 and the polyamine putrescine is a key product of this pathway in other bacteria. Interestingly, different polyamines are produced by both fish and invertebrate tissue decay and to accumulate especially in shrimp hepatopancreatic tissue from fish based feed with no adverse effects. Polyamines are an attractant for some bacteria like Pseudomonas but the role of these in Vibrio chemotaxis is not known. Exogenous polyamines produced by eukaryotes and prokaryotes are shown to enhance biofilm production in V. cholerae. These transcriptional insights may provide clues about how these bacteria interact and may even identify candidate attractant molecules.
Two separate operons were upregulated in Ta Mai more than 1000-fold. GO annotations were not assigned to these genes thus they were not included in the hypergeometric and GSEA analyses. One gene (TMChrII_2378) encodes a protein with high structural conservation to heme monooxgenase and the other (TMChrI_2040) a dioxygenase that closely resembles a bleomycin resistance proteins. A second dioxygenase (TMChr1_3001) is also among the top induced genes. This family of dioxygenase proteins includes those that can bind and in some cases hydrolyze planar and aromatic antibacterial molecules including phenazines. Though amino acid sequence similarity is poor, the predicted structure of TMChr1_2040 is very similar to EphR, a protein that loosely binds phenazine in producer strains and confers resistance by binding molecules until export. To test whether these proteins are operative in resistance, both were cloned and expressed into the V. cholerae O1 strain, H1, a strain very sensitive to the A603 phenazine. Only TMChr1_2040 is shown to confer partial resistance, demonstrating its role is likely similar to other EphR proteins.
Killing assays, genetic approaches and the completed genome of Aeromonas hydrophila A603 were used to identify the T6SS and phenazine biosynthesis operons and determined both are operative, distinct antibacterial mechanisms. Both kill or inhibit the growth of all tested bacteria of the genus Vibrio, including EMS strains isolated from infected and diseased shrimp sourced from Thailand. This antibacterial activity is significantly robust in vitro when large numbers of both predatory A603 and prey Vibrio are incubated together, enough that 10-100 million bacteria are killed in a couple hours. It is worth noting that spontaneous T6SS resistance has yet to be found in any T6SS susceptible gram-negative strain to its competent “predator” strain.
When shrimp were infected with A603 by inoculating environmental water, a low level colonization could be measured with a small effect on the natural shrimp microbiome. In contrast, shrimp infected with EMS-related Vibrio strains exhibited significant dysbiosis with an exponential increase of Vibrio and significant reduction of bacterial diversity. Shrimp pretreated with A603 T6SS+ were largely protected from colonization by EMS and dysbiosis. This protection was significantly reduced by using an A603 T6SS mutant (A603 ΔvipA) suggesting T6SS is a key component of the probiotic effect. When shrimp are treated with EMS, death occurs >80% within one week and with A603 or A603+ EMS mortality was never observed to be more frequent than uninfected (<10% per week, data not shown). These observations suggest A603 is competent for colonizing shrimp via natural uptake from environmental water and that this colonization is not harmful to shrimp or disruptive to the natural shrimp microbiome. Furthermore this provides an advantage to shrimp in that it protects from the colonization by pathogenic strains of Vibrio parahaemolyticus known to cause EMS.
The bacterial inoculum (105-6 cfu/ml) used for protection in these small scale shrimp challenges can easily be scaled up for large tanks or ponds (
The micriobiome of AHPND-infected shrimp shows a modest 3-fold increase of bacteria in the Vibrionaceae 72 hours post-infection when compared to DNA reads that are map to about 80 other bacterial families. The increase of mapped DNA to Vibrionaceae in the shrimp body is more than that measured in the hepatopancreas.
RNA extracted and sequenced from the same shrimp shows a significant increase of recovered RNA from the shrimp body, but not the hepatopancreatic tissue. This result suggests bacteria in the Vibrionaceae are much more metabolically active in infected shrimp and that colonization is not specific to the hepatopancreatic tissue, which is where most disease tissue damage has been observed for this bacterial disease.
Furthermore, DNA from live or dead cells or that which has been released into the environment cannot be distinguished, but RNA is easily degraded and unstable when released from dead cells. As bacterial chromosomal DNA usually exists as a single copy per cell and the abundance of RNA transcripts per gene is found to vary from less than one to over 50,000 for ribosomal RNA. The greater abundance for RNA suggests these bacteria are alive and metabolically active (
Transcriptome (RNA sequencing) of the shrimp body is the best indicator of the increased bacterial load of Vibrionaceae. Using this metric, it is shown that a 24-fold increase of Vibrionaceae bacteria in infected shrimp after 72 hours. The only other bacteria family that appears to track closely with Vibrio-related species in abundance are those in the Aeromonadaceae. By sequence, these Aeromonas bacteria are not the A603 strain and do not appear to eliminate Vibrio from shrimp, but the observation indicates that AHPND-infected shrimp may become more vulnerable to colonization by Aeromonads (
Using the transcriptome data, shrimp pretreated with A603 have 3-fold fewer Vibrionaceae and 8-fold fewer Aeromonadaceae after 72 hours. There are three shrimp per group in the experiment and each plot point represents the average abundance of bacterial family as in
The data from these independent groups shows the same coincidental tracking of Vibrionaceae with Aeromonadaceae, but in the first groups (
Because other species, strains, and serotypes of Aeromonas and Vibrio, in addition to V. parahaemolyticus, cause disease in shellfish, fish, and humans, A603 could be a used as preventive treatment for a number of pathogens. These include, but are not limited to, V. vulnificus, V. harveyi, V. cholerae, V. aliginolyticus, A. hydrophila, and A. media. Every representative isolate of Vibrio and Aeromonas species in this list of six have been shown to be killed by A603. A603 does appear to have either minor or no impact on most bacteria families in shrimp confirming the antibacterial activity is targeted to bacteria families that includes many species that cause disease (
Protection in shrimp was qualified using NGS sequencing. Protection in A603 can be measured by a marked quantitative reduction in V. parahaemolyticus (or Vibrio) in shrimp. Bacteria extracted from shrimp were sequenced using NGS (Illumina) and A603 and V. parahaemolyticus were quantified against an added DNA standard.
The following table shows upregulated pathways in V. parahaemolyticus EMS strain depend on T6SS and phenazine.
All publications, patents, and patent applications mentioned herein are hereby incorporated by reference in their entirety as if each individual publication, patent or patent application was specifically and individually indicated to be incorporated by reference. In case of conflict, the present application, including any definitions herein, will control.
Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention described herein. Such equivalents are intended to be encompassed by the following claims.
This application claims priority to U.S. Provisional Application 62/632,085 filed Feb. 19, 2018, and U.S. Provisional Application 62/632,729, filed Feb. 20, 2018, each of which is incorporated herein by reference in its entirety
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US2019/018563 | 2/19/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62632085 | Feb 2018 | US | |
| 62632729 | Feb 2018 | US |
