Patent Application
20200115765
Incorporated by reference in its entirety herein is a computer-readable nucleotide sequence listing submitted concurrently herewith and identified as follows: One 3,419 Byte ASCII (Text) file named “USGS_17-010_SEQ.txt,” created on Oct. 3, 2018.
This invention relates to the field of nucleic acid products used in the analysis of nucleic acids, such as primers or probes for detection or identification of organisms and more specifically to an assay for testing for Asian Carp.
The U.S. Geological Survey (USGS) is a bureau of the Department of the Interior with a mission to provide time-sensitive scientific data about the nation's geological resources as crises are occurring. The role of the USGS is critical to support federal agencies in protecting lakes, rivers and tributaries from the effects of Asian Carp. Asian Carp are prohibited invasive species which cause irreversible ecosystem damage and potentially render the environment inhospitable to the $7 billion per year fishing industry. Introduction of Asian Carp into an ecosystem can eradicate native fish populations in a matter of years.
In 2017, the USGS began working with U.S. Fish and Wildlife biologists and law enforcement agencies to develop rapid in situ test kits to detect the presence of prohibited species such as Asian Carp.
Several states have passed regulations to control human commercial activity that can introduce Asian carp into previously unaffected areas, such as transporting bait. Despite these measures, Asian Carp are expected to spread to 31 states by the end of 2019. Multiple agencies have collaborated to control the spread of Asian Carp.
There are currently ten species of Asian Carp on the government's prohibited species list. On this list, the most prevalent species is the grass carp; silver carp ranks fourth, bighead carp ranks sixth, and black carp ranks seventh.
In 2015, a published study concluded that 1 out of 550 Midwestern bait shops tested positive for genetic material from Asian Carp.
PCR tests are known in the art, which can test for Asian Carp DNA.
It is a problem known in the art that PCR testing is expensive. These tests must be conducted in a professional laboratory and require a series of alternating temperature steps or cycles. The equipment required to conduct the PCR testing is costly, and testing cannot be conducted on site.
Recently developed loop-mediated isothermal amplification (LAMP) tests can be run on-site at one constant temperature without the need for expensive equipment.
There is an unmet need for rapid, on-site testing methods that can be used to detect multiple species of Asian Carp.
The invention uses the loop-mediated isothermal amplification (LAMP) method of DNA amplification to detect the presence of Asian Carp, including the following species: Hypophthalmichthys nobilis, H. molitrix, Ctenopharyngodon idella, Mylopharyngodon piceus.
The LAMP primers disclosed are designed to anneal to mitochondrial DNA sequences only found in Asian Carp to initiate replication of that segment of DNA. As the replication continues, a fluorescent dye intercalates into the double-stranded DNA products and fluoresces at a known wavelength. This fluorescent light is detected by the any instrument used to analyze the samples. An increase in fluorescent signal intensity over time indicates the presence of the target DNA sequence.
As used herein, the term “LAMP apparatus” means any test which detects DNA and which does not require multiple cycles of temperature changes for amplification.
As used herein, the term “potential degenerate base sequence” means a sequence position that is either specifically defined as one nucleotide base or which can be one of two bases. If a primer sequence includes a degenerate base, it is shown as R for purine bases or Y for pyrimidine bases. Purine bases include guanine or adenine, meaning that an R in the primer sequence represents either a G or an A. Pyrimidine bases include cytosine or thymine, meaning that a Y in the primer sequence represents either a C or a T.
LAMP apparatus 100 further includes reagents, which include but are not limited to enzymes, pH buffers, triphosphate dNTPs, magnesium salt, and dyes known in the art to replicate the target DNA sequence and dye the replicated DNA to make the copies visible to a machine. LAMP assay apparatus 100 can utilize any LAMP assay result detection method known in the art. In various embodiments, LAMP assay apparatus 100 can dye replicated DNA copies to make them visible to the human eye.
In the embodiment shown, primers, enzymes, and dyes are combined with a sample in a reaction tube and incubated at a constant temperature for a user-determined period of time. The sample may either include an unknown number of copies of the target DNA sequence, or a known number of copies of the target DNA sequence.
In the exemplary embodiment shown, some of the primer sequence positions can have one of two bases, known as degenerate bases. If a primer sequence includes a degenerate base, it is shown as R for purine bases or Y for pyrimidine bases. Purine bases include guanine or adenine, meaning that an R in the primer sequence represents either a G or an A. Pyrimidine bases include cytosine or thymine, meaning that a Y in the primer sequence represents either a C or a T.
In the exemplary embodiment shown, the primers listed in
In the exemplary embodiment shown, the oligonucleotide primers detect Asian Carp species, including but not limited to the following species Hypophthalmichthys nobilis, H. molitrix, Ctenopharyngodon idella, and Mylopharyngodon piceus. These species are commonly known as Bighead Carp, Silver Carp, Grass Carp, and Black Carp, respectively.
The table in
Step 1 is the step of obtaining a test sample to be tested for the presence of Asian Carp genetic material.
In the exemplary embodiment, a test sample is a quantity of DNA extracted from sampled water that may have contained Asian Carp. This step may include any method known in the art for extracting DNA from a water sample. Assay apparatus 100 detects Asian Carp genetic material in the test sample, whether or not the fish is still present in the sampled container at the time of obtaining the sampled water. In various embodiments, a single fish sheds enough DNA to be detected by the test.
In various embodiments, LAMP assay apparatus 100 can detect a single Silver Carp in a pool of 33,000 flathead minnows.
In still other embodiments, LAMP assay apparatus 100 may detect as few as 10 DNA copies per 40 μL LAMP reaction.
Step 2 is the step of obtaining a positive control sample and negative control sample for comparison. In various embodiments, a positive control sample may be included in LAMP assay apparatus 100.
In all embodiments, a positive control sample has at least a minimum number of Asian Carp DNA copies. In various embodiments, the minimum number of DNA copies may be 10 DNA copies per 40 μL LAMP reaction.
Using LAMP assay apparatus 100 on this positive control sample will result in a fluorescent signal. The negative control sample has no Asian Carp DNA copies and using LAMP assay apparatus 100 on this negative control sample will not result in a fluorescent signal. After using LAMP assay apparatus 100 on the test samples and control samples, the results will be compared to determine which test samples resulted in a fluorescent signal, indicating that the test samples contain Asian Carp DNA.
In various embodiments, the positive control sample will indicate that the LAMP reagents (reaction components) are working properly. If the reaction with the positive control sample does not show a fluorescent signal, then the LAMP reagents may need to be replaced.
In various embodiments, a fluorescent signal in the negative control reaction will indicate that the assay has resulted in false positives and needs to be repeated with replaced reagents.
Step 3 is the step of selecting an effective concentration of each of the following primers.
In one exemplary embodiment, the LAMP primer set binds to Asian Carp DNA and includes the following sequences (as illustrated in
a forward primer having the following sequence: 5′-TTCCCCTAACARTATCAGGCT-3′ <SEQ ID NO. 5> or <SEQ ID NO. 6>;
a forward inner primer having the following sequence: 5′-AGTGGTTTGTCCGATCTGGTCATGGAAGAAATTATGCTAAAATG-3′ <SEQ ID NO. 7>;
a backward primer having the following sequence 5′-TAGCACTCCRGTGTGGGGT-3′ <SEQ ID NO. 8> or <SEQ ID NO. 9>;
a backward inner primer having the following sequence 5′-ATTAACGAACTCAACCCAAGAACGATTGTTTAATTGTGGGTTT-3′ <SEQ ID NO. 10>;
a forward loop primer having the following sequence 5′-CTTGGAGAAGAGCAGGTCT-3′ <SEQ ID NO. 11>; and
a backward loop primer having the following sequence 5′-GAGTAATGTRAAYAACAAAAAAACC-3′ <SEQ ID NO. 12>, <SEQ ID NO. 13>, <SEQ ID NO. 14>, or <SEQ ID NO. 15>.
In the exemplary embodiment shown in
Step 4 is the step of selecting a constant temperature.
In the exemplary embodiment, the constant LAMP reaction temperature is approximately 55 to 70° C. In various embodiments, the optimal constant LAMP reaction temperature is 62.9° C.
Step 5 is the step of performing a LAMP assay at a constant LAMP reaction temperature of approximately 55 to 70° C. In various embodiments, the optimal constant LAMP reaction temperature is 62.9° C.
To perform the LAMP assay, each test sample, positive control sample, and negative control sample is placed in a separate reaction tube. Each reaction tube also receives enzymes and dyes known in the art and the novel primer set. The reaction tubes are incubated at the constant temperature chosen in Step 5. The user determines the time period for incubation based on manufacturer instruction. The concentration of each sample and each commercially available component in the reaction tube is determined by the user, according to manufacturer recommendations. The reaction concentration of each primer was determined by the user in Step 4.
The invention uses loop-mediated isothermal amplification of DNA. The LAMP primers anneal to a segment of Asian Carp mitochondrial DNA to initiate replication of the segment. As the replication continues, a fluorescent dye intercalates into the double-stranded DNA products and fluoresces at a known wavelength. This fluorescent light is detected by any instrument used to analyze the samples, and increasing fluorescent signal intensity over time indicates the presence of the target DNA.
In various embodiments, various commercially available enzymes, buffers, coenzymes, adjuvants, dyes, and deoxyribonucleic acids can be used to run assay apparatus 100. One exemplary embodiment may utilize the commercially available reagent Isothermal Master Mix (ISO-004) from Pro Lab Diagnostics.
Step 6 is the step of comparing the result of each test sample to the result of the positive and negative control samples to determine if a minimum threshold is exceeded. In various embodiments, using assay apparatus 100 on the positive control sample will result in a fluorescent signal. Using assay apparatus 100 on a test sample with a number of Asian Carp DNA copies that exceeds the minimum threshold will result in a fluorescent signal significantly more intense than the intensity of the background fluorescent signal, as determined by the user. In various embodiments, the minimum detectible threshold is 10 copies per 40 μL LAMP reaction. In various embodiments, the fluorescent signal is detectable by a machine.
