In JoVE (2)

Other Publications (27)

Articles by Roger S. Lasken in JoVE

Other articles by Roger S. Lasken on PubMed

A Full-coverage, High-resolution Human Chromosome 22 Genomic Microarray for Clinical and Research Applications

Human Molecular Genetics. Dec, 2002  |  Pubmed ID: 12444106

We have constructed the first comprehensive microarray representing a human chromosome for analysis of DNA copy number variation. This chromosome 22 array covers 34.7 Mb, representing 1.1% of the genome, with an average resolution of 75 kb. To demonstrate the utility of the array, we have applied it to profile acral melanoma, dermatofibrosarcoma, DiGeorge syndrome and neurofibromatosis 2. We accurately diagnosed homozygous/heterozygous deletions, amplifications/gains, IGLV/IGLC locus instability, and breakpoints of an imbalanced translocation. We further identified the 14-3-3 eta isoform as a candidate tumor suppressor in glioblastoma. Two significant methodological advances in array construction were also developed and validated. These include a strictly sequence defined, repeat-free, and non-redundant strategy for array preparation. This approach allows an increase in array resolution and analysis of any locus; disregarding common repeats, genomic clone availability and sequence redundancy. In addition, we report that the application of phi29 DNA polymerase is advantageous in microarray preparation. A broad spectrum of issues in medical research and diagnostics can be approached using the array. This well annotated and gene-rich autosome contains numerous uncharacterized disease genes. It is therefore crucial to associate these genes to specific 22q-related conditions and this array will be instrumental towards this goal. Furthermore, comprehensive epigenetic profiling of 22q-located genes and high-resolution analysis of replication timing across the entire chromosome can be studied using our array.

Comprehensive Human Genome Amplification Using Multiple Displacement Amplification

Proceedings of the National Academy of Sciences of the United States of America. Apr, 2002  |  Pubmed ID: 11959976

Fundamental to most genetic analysis is availability of genomic DNA of adequate quality and quantity. Because DNA yield from human samples is frequently limiting, much effort has been invested in developing methods for whole genome amplification (WGA) by random or degenerate oligonucleotide-primed PCR. However, existing WGA methods like degenerate oligonucleotide-primed PCR suffer from incomplete coverage and inadequate average DNA size. We describe a method, termed multiple displacement amplification (MDA), which provides a highly uniform representation across the genome. Amplification bias among eight chromosomal loci was less than 3-fold in contrast to 4-6 orders of magnitude for PCR-based WGA methods. Average product length was >10 kb. MDA is an isothermal, strand-displacing amplification yielding about 20-30 microg product from as few as 1-10 copies of human genomic DNA. Amplification can be carried out directly from biological samples including crude whole blood and tissue culture cells. MDA-amplified human DNA is useful for several common methods of genetic analysis, including genotyping of single nucleotide polymorphisms, chromosome painting, Southern blotting and restriction fragment length polymorphism analysis, subcloning, and DNA sequencing. MDA-based WGA is a simple and reliable method that could have significant implications for genetic studies, forensics, diagnostics, and long-term sample storage.

Whole Genome Amplification: Abundant Supplies of DNA from Precious Samples or Clinical Specimens

Trends in Biotechnology. Dec, 2003  |  Pubmed ID: 14624861

High Accuracy Genotyping Directly from Genomic DNA Using a Rolling Circle Amplification Based Assay

BMC Genomics. May, 2003  |  Pubmed ID: 12777185

Rolling circle amplification of ligated probes is a simple and sensitive means for genotyping directly from genomic DNA. SNPs and mutations are interrogated with open circle probes (OCP) that can be circularized by DNA ligase when the probe matches the genotype. An amplified detection signal is generated by exponential rolling circle amplification (ERCA) of the circularized probe. The low cost and scalability of ligation/ERCA genotyping makes it ideally suited for automated, high throughput methods.

Unbiased Whole-genome Amplification Directly from Clinical Samples

Genome Research. May, 2003  |  Pubmed ID: 12695328

Preparation of genomic DNA from clinical samples is a bottleneck in genotyping and DNA sequencing analysis and is frequently limited by the amount of specimen available. We use Multiple Displacement Amplification (MDA) to amplify the whole genome 10,000-fold directly from small amounts of whole blood, dried blood, buccal cells, cultured cells, and buffy coats specimens, generating large amounts of DNA for genetic testing. Genomic DNA was evenly amplified with complete coverage and consistent representation of all genes. All 47 loci analyzed from 44 individuals were represented in the amplified DNA at between 0.5- and 3.0-fold of the copy number in the starting genomic DNA template. A high-fidelity DNA polymerase ensures accurate representation of the DNA sequence. The amplified DNA was indistinguishable from the original genomic DNA template in 5 SNP and 10 microsatellite DNA assays on three different clinical sample types for 20 individuals. Amplification of genomic DNA directly from cells is highly reproducible, eliminates the need for DNA template purification, and allows genetic testing from small clinical samples. The low amplification bias of MDA represents a dramatic technical improvement in the ability to amplify a whole genome compared with older, PCR-based methods.

Two Methods of Whole-genome Amplification Enable Accurate Genotyping Across a 2320-SNP Linkage Panel

Genome Research. May, 2004  |  Pubmed ID: 15123587

Comprehensive genome scans involving many thousands of SNP assays will require significant amounts of genomic DNA from each sample. We report two successful methods for amplifying whole-genomic DNA prior to SNP analysis, multiple displacement amplification, and OmniPlex technology. We determined the coverage of amplification by analyzing a SNP linkage marker set that contained 2320 SNP markers spread across the genome at an average distance of 2.5 cM. We observed a concordance of >99.8% in genotyping results from genomic DNA and amplified DNA, strongly indicating the ability of both methods used to amplify genomic DNA in a highly representative manner. Furthermore, we were able to achieve a SNP call rate of >98% in both genomic and amplified DNA. The combination of whole-genome amplification and comprehensive SNP linkage analysis offers new opportunities for genetic analysis in clinical trials, disease association studies, and archiving of DNA samples.

Genomic DNA Amplification from a Single Bacterium

Applied and Environmental Microbiology. Jun, 2005  |  Pubmed ID: 15933038

Genomic DNA was amplified about 5 billion-fold from single, flow-sorted bacterial cells by the multiple displacement amplification (MDA) reaction, using phi 29 DNA polymerase. A 662-bp segment of the 16S rRNA gene could be accurately sequenced from the amplified DNA. MDA methods enable new strategies for studying non-culturable microorganisms.

Single-cell Genomic Sequencing Using Multiple Displacement Amplification

Current Opinion in Microbiology. Oct, 2007  |  Pubmed ID: 17923430

Single microbial cells can now be sequenced using DNA amplified by the Multiple Displacement Amplification (MDA) reaction. The few femtograms of DNA in a bacterium are amplified into micrograms of high molecular weight DNA suitable for DNA library construction and Sanger sequencing. The MDA-generated DNA also performs well when used directly as template for pyrosequencing by the 454 Life Sciences method. While MDA from single cells loses some of the genomic sequence, this approach will greatly accelerate the pace of sequencing from uncultured microbes. The genetically linked sequences from single cells are also a powerful tool to be used in guiding genomic assembly of shotgun sequences of multiple organisms from environmental DNA extracts (metagenomic sequences).

Nanoliter Reactors Improve Multiple Displacement Amplification of Genomes from Single Cells

PLoS Genetics. Sep, 2007  |  Pubmed ID: 17892324

Since only a small fraction of environmental bacteria are amenable to laboratory culture, there is great interest in genomic sequencing directly from single cells. Sufficient DNA for sequencing can be obtained from one cell by the Multiple Displacement Amplification (MDA) method, thereby eliminating the need to develop culture methods. Here we used a microfluidic device to isolate individual Escherichia coli and amplify genomic DNA by MDA in 60-nl reactions. Our results confirm a report that reduced MDA reaction volume lowers nonspecific synthesis that can result from contaminant DNA templates and unfavourable interaction between primers. The quality of the genome amplification was assessed by qPCR and compared favourably to single-cell amplifications performed in standard 50-microl volumes. Amplification bias was greatly reduced in nanoliter volumes, thereby providing a more even representation of all sequences. Single-cell amplicons from both microliter and nanoliter volumes provided high-quality sequence data by high-throughput pyrosequencing, thereby demonstrating a straightforward route to sequencing genomes from single cells.

Sequence Specific Detection of DNA Using Nicking Endonuclease Signal Amplification (NESA)

Nucleic Acids Research. 2007  |  Pubmed ID: 17827214

We have developed a new method for identifying specific single- or double-stranded DNA sequences called nicking endonuclease signal amplification (NESA). A probe and target DNA anneal to create a restriction site that is recognized by a strand-specific endonuclease that cleaves the probe into two pieces leaving the target DNA intact. The target DNA can then act as a template for fresh probe and the process of hybridization, cleavage and dissociation repeats. Laser-induced fluorescence coupled with capillary electrophoresis was used to measure the probe cleavage products. The reaction is rapid; full cleavage of probe occurs within one minute under ideal conditions. The reaction is specific since it requires complete complementarity between the oligonucleotide and the template at the restriction site and sufficient complementarity overall to allow hybridization. We show that both Bacillus subtilis and B. anthracis genomic DNA can be detected and specifically differentiated from DNA of other Bacillus species. When combined with multiple displacement amplification, detection of a single copy target from less than 30 cfu is possible. This method should be applicable whenever there is a requirement to detect a specific DNA sequence. Other applications include SNP analysis and genotyping. The reaction is inherently simple to multiplex and is amenable to automation.

Insights into the Genome of Large Sulfur Bacteria Revealed by Analysis of Single Filaments

PLoS Biology. Sep, 2007  |  Pubmed ID: 17760503

Marine sediments are frequently covered by mats of the filamentous Beggiatoa and other large nitrate-storing bacteria that oxidize hydrogen sulfide using either oxygen or nitrate, which they store in intracellular vacuoles. Despite their conspicuous metabolic properties and their biogeochemical importance, little is known about their genetic repertoire because of the lack of pure cultures. Here, we present a unique approach to access the genome of single filaments of Beggiatoa by combining whole genome amplification, pyrosequencing, and optical genome mapping. Sequence assemblies were incomplete and yielded average contig sizes of approximately 1 kb. Pathways for sulfur oxidation, nitrate and oxygen respiration, and CO2 fixation confirm the chemolithoautotrophic physiology of Beggiatoa. In addition, Beggiatoa potentially utilize inorganic sulfur compounds and dimethyl sulfoxide as electron acceptors. We propose a mechanism of vacuolar nitrate accumulation that is linked to proton translocation by vacuolar-type ATPases. Comparative genomics indicates substantial horizontal gene transfer of storage, metabolic, and gliding capabilities between Beggiatoa and cyanobacteria. These capabilities enable Beggiatoa to overcome non-overlapping availabilities of electron donors and acceptors while gliding between oxic and sulfidic zones. The first look into the genome of these filamentous sulfur-oxidizing bacteria substantially deepens the understanding of their evolution and their contribution to sulfur and nitrogen cycling in marine sediments.

Mechanism of Chimera Formation During the Multiple Displacement Amplification Reaction

BMC Biotechnology. 2007  |  Pubmed ID: 17430586

Multiple Displacement Amplification (MDA) is a method used for amplifying limiting DNA sources. The high molecular weight amplified DNA is ideal for DNA library construction. While this has enabled genomic sequencing from one or a few cells of unculturable microorganisms, the process is complicated by the tendency of MDA to generate chimeric DNA rearrangements in the amplified DNA. Determining the source of the DNA rearrangements would be an important step towards reducing or eliminating them.

Specific Single-cell Isolation and Genomic Amplification of Uncultured Microorganisms

Applied Microbiology and Biotechnology. Mar, 2007  |  Pubmed ID: 17109170

We in this study describe a new method for genomic studies of individual uncultured prokaryotic organisms, which was used for the isolation and partial genome sequencing of a soil archaeon. The diversity of Archaea in a soil sample was mapped by generating a clone library using group-specific primers in combination with a terminal restriction fragment length polymorphism profile. Intact cells were extracted from the environmental sample, and fluorescent in situ hybridization probing with Cy3-labeled probes designed from the clone library was subsequently used to detect the organisms of interest. Single cells with a bright fluorescent signal were isolated using a micromanipulator and the genome of the single isolated cells served as a template for multiple displacement amplification (MDA) using the Phi29 DNA polymerase. The generated MDA product was afterwards used for 16S rRNA gene sequence analysis and shotgun-cloned for additional genomic analysis. Sequence analysis showed >99% 16S rRNA gene homology to soil crenarchaeotal clone SCA1170 and shotgun fragments had the closest match to a crenarchaeotal BAC clone previously retrieved from a soil sample. The system was validated using Methanothermobacter thermoautotrophicus as single-cell test organism, and the validation setup produced 100% sequence homology to the ten tested regions of the genome of this organism.

Genomic Sequencing of Single Microbial Cells from Environmental Samples

Current Opinion in Microbiology. Jun, 2008  |  Pubmed ID: 18550420

Recently developed techniques allow genomic DNA sequencing from single microbial cells [Lasken RS: Single-cell genomic sequencing using multiple displacement amplification. Curr Opin Microbiol 2007, 10:510-516]. Here, we focus on research strategies for putting these methods into practice in the laboratory setting. An immediate consequence of single-cell sequencing is that it provides an alternative to culturing organisms as a prerequisite for genomic sequencing. The microgram amounts of DNA required as template are amplified from a single bacterium by a method called multiple displacement amplification (MDA) avoiding the need to grow cells. The ability to sequence DNA from individual cells will likely have an immense impact on microbiology considering the vast numbers of novel organisms, which have been inaccessible unless culture-independent methods could be used. However, special approaches have been necessary to work with amplified DNA. MDA may not recover the entire genome from the single copy present in most bacteria. Also, some sequence rearrangements can occur during the DNA amplification reaction. Over the past two years many research groups have begun to use MDA, and some practical approaches to single-cell sequencing have been developed. We review the consensus that is emerging on optimum methods, reliability of amplified template, and the proper interpretation of 'composite' genomes which result from the necessity of combining data from several single-cell MDA reactions in order to complete the assembly. Preferred laboratory methods are considered on the basis of experience at several large sequencing centers where >70% of genomes are now often recovered from single cells. Methods are reviewed for preparation of bacterial fractions from environmental samples, single-cell isolation, DNA amplification by MDA, and DNA sequencing.

Something from (almost) Nothing: the Impact of Multiple Displacement Amplification on Microbial Ecology

The ISME Journal. Mar, 2008  |  Pubmed ID: 18256705

Microbial ecology is a field that applies molecular techniques to analyze genes and communities associated with a plethora of unique environments on this planet. In the past, low biomass and the predominance of a few abundant community members have impeded the application of techniques such as PCR, microarray analysis and metagenomics to complex microbial populations. In the absence of suitable cultivation methods, it was not possible to obtain DNA samples from individual microorganisms. Recently, a method called multiple displacement amplification (MDA) has been used to circumvent these limitations by amplifying DNA from microbial communities in low-biomass environments, individual cells from uncultivated microbial species and active organisms obtained through stable isotope probing incubations. This review describes the development and applications of MDA, discusses its strengths and limitations and highlights the impact of MDA on the field of microbial ecology. Whole genome amplification via MDA has increased access to the genomic DNA of uncultivated microorganisms and low-biomass environments and represents a 'power tool' in the molecular toolbox of microbial ecologists.

Genomic DNA Amplification by the Multiple Displacement Amplification (MDA) Method

Biochemical Society Transactions. Apr, 2009  |  Pubmed ID: 19290880

Large amounts of DNA are frequently required for use in detection assays and genomic analysis. The limited availability of DNA can be a critical obstacle to meeting research and clinical needs. DNA amplification methods are often required to generate sufficient material from small specimens or environmental samples with low DNA content. The MDA (multiple displacement amplification) reaction is increasingly the method of choice for many applications because of its extensive coverage of the genome, the generation of extremely long DNA products compared with older whole genome amplification methods and the high DNA yields, even from exceedingly low amounts of starting material. Remarkably, MDA enables genomic sequencing even from single microbial cells. Some of the uses of MDA and its strengths and limitations will be discussed.

Multiple Displacement Amplification As an Adjunct to PCR-based Detection of Staphylococcus Aureus in Synovial Fluid

BMC Research Notes. 2010  |  Pubmed ID: 20942932

Detection of bacterial nucleic acids in synovial fluid following total joint arthroplasty with suspected infection can be difficult; among other technical challenges, inhibitors in the specimens require extensive sample preparation and can diminish assay sensitivity even using polymerase chain reaction (PCR)-based methods. To address this problem a simple protocol for prior use of multiple displacement amplification (MDA) as an adjunct to PCR was established and tested on both purified S. aureus DNA as well as on clinical samples known to contain S. aureus nucleic acids.

Targeted Metagenomics and Ecology of Globally Important Uncultured Eukaryotic Phytoplankton

Proceedings of the National Academy of Sciences of the United States of America. Aug, 2010  |  Pubmed ID: 20668244

Among eukaryotes, four major phytoplankton lineages are responsible for marine photosynthesis; prymnesiophytes, alveolates, stramenopiles, and prasinophytes. Contributions by individual taxa, however, are not well known, and genomes have been analyzed from only the latter two lineages. Tiny "picoplanktonic" members of the prymnesiophyte lineage have long been inferred to be ecologically important but remain poorly characterized. Here, we examine pico-prymnesiophyte evolutionary history and ecology using cultivation-independent methods. 18S rRNA gene analysis showed pico-prymnesiophytes belonged to broadly distributed uncultivated taxa. Therefore, we used targeted metagenomics to analyze uncultured pico-prymnesiophytes sorted by flow cytometry from subtropical North Atlantic waters. The data reveal a composite nuclear-encoded gene repertoire with strong green-lineage affiliations, which contrasts with the evolutionary history indicated by the plastid genome. Measured pico-prymnesiophyte growth rates were rapid in this region, resulting in primary production contributions similar to the cyanobacterium Prochlorococcus. On average, pico-prymnesiophytes formed 25% of global picophytoplankton biomass, with differing contributions in five biogeographical provinces spanning tropical to subpolar systems. Elements likely contributing to success include high gene density and genes potentially involved in defense and nutrient uptake. Our findings have implications reaching beyond pico-prymnesiophytes, to the prasinophytes and stramenopiles. For example, prevalence of putative Ni-containing superoxide dismutases (SODs), instead of Fe-containing SODs, seems to be a common adaptation among eukaryotic phytoplankton for reducing Fe quotas in low-Fe modern oceans. Moreover, highly mosaic gene repertoires, although compositionally distinct for each major eukaryotic lineage, now seem to be an underlying facet of successful marine phytoplankton.

Efficient De Novo Assembly of Single-cell Bacterial Genomes from Short-read Data Sets

Nature Biotechnology. Oct, 2011  |  Pubmed ID: 21926975

Whole genome amplification by the multiple displacement amplification (MDA) method allows sequencing of DNA from single cells of bacteria that cannot be cultured. Assembling a genome is challenging, however, because MDA generates highly nonuniform coverage of the genome. Here we describe an algorithm tailored for short-read data from single cells that improves assembly through the use of a progressively increasing coverage cutoff. Assembly of reads from single Escherichia coli and Staphylococcus aureus cells captures >91% of genes within contigs, approaching the 95% captured from an assembly based on many E. coli cells. We apply this method to assemble a genome from a single cell of an uncultivated SAR324 clade of Deltaproteobacteria, a cosmopolitan bacterial lineage in the global ocean. Metabolic reconstruction suggests that SAR324 is aerobic, motile and chemotaxic. Our approach enables acquisition of genome assemblies for individual uncultivated bacteria using only short reads, providing cell-specific genetic information absent from metagenomic studies.

Genomic Insights into the Physiology and Ecology of the Marine Filamentous Cyanobacterium Lyngbya Majuscula

Proceedings of the National Academy of Sciences of the United States of America. May, 2011  |  Pubmed ID: 21555588

Filamentous cyanobacteria of the genus Lyngbya are important contributors to coral reef ecosystems, occasionally forming dominant cover and impacting the health of many other co-occurring organisms. Moreover, they are extraordinarily rich sources of bioactive secondary metabolites, with 35% of all reported cyanobacterial natural products deriving from this single pantropical genus. However, the true natural product potential and life strategies of Lyngbya strains are poorly understood because of phylogenetic ambiguity, lack of genomic information, and their close associations with heterotrophic bacteria and other cyanobacteria. To gauge the natural product potential of Lyngbya and gain insights into potential microbial interactions, we sequenced the genome of Lyngbya majuscula 3L, a Caribbean strain that produces the tubulin polymerization inhibitor curacin A and the molluscicide barbamide, using a combination of Sanger and 454 sequencing approaches. Whereas ∼ 293,000 nucleotides of the draft genome are putatively dedicated to secondary metabolism, this is far too few to encode a large suite of Lyngbya metabolites, suggesting Lyngbya metabolites are strain specific and may be useful in species delineation. Our analysis revealed a complex gene regulatory network, including a large number of sigma factors and other regulatory proteins, indicating an enhanced ability for environmental adaptation or microbial associations. Although Lyngbya species are reported to fix nitrogen, nitrogenase genes were not found in the genome or by PCR of genomic DNA. Subsequent growth experiments confirmed that L. majuscula 3L is unable to fix atmospheric nitrogen. These unanticipated life history characteristics challenge current views of the genus Lyngbya.

Single Virus Genomics: a New Tool for Virus Discovery

PloS One. 2011  |  Pubmed ID: 21436882

Whole genome amplification and sequencing of single microbial cells has significantly influenced genomics and microbial ecology by facilitating direct recovery of reference genome data. However, viral genomics continues to suffer due to difficulties related to the isolation and characterization of uncultivated viruses. We report here on a new approach called 'Single Virus Genomics', which enabled the isolation and complete genome sequencing of the first single virus particle. A mixed assemblage comprised of two known viruses; E. coli bacteriophages lambda and T4, were sorted using flow cytometric methods and subsequently immobilized in an agarose matrix. Genome amplification was then achieved in situ via multiple displacement amplification (MDA). The complete lambda phage genome was recovered with an average depth of coverage of approximately 437X. The isolation and genome sequencing of uncultivated viruses using Single Virus Genomics approaches will enable researchers to address questions about viral diversity, evolution, adaptation and ecology that were previously unattainable.

Genomic Sequencing of Uncultured Microorganisms from Single Cells

Nature Reviews. Microbiology. Sep, 2012  |  Pubmed ID: 22890147

Sequencing DNA from single cells has opened new windows onto the microbial world. It is becoming routine to sequence bacterial species directly from environmental samples or clinical specimens without the need to develop cultivation methods. Recent technical improvements often allow nearly complete genome assembly from these otherwise inaccessible species. New bioinformatics methods are also improving genome assembly from single cells. The use of single-cell sequencing in combination with metagenomic analysis is also emerging as a powerful new strategy to analyse bacterial communities. Here, the technical developments that have enabled single-cell sequencing, as well as some of the most exciting applications of this approach from the past few years, are reviewed.

Genomic Insights to SAR86, an Abundant and Uncultivated Marine Bacterial Lineage

The ISME Journal. Jun, 2012  |  Pubmed ID: 22170421

Bacteria in the 16S rRNA clade SAR86 are among the most abundant uncultivated constituents of microbial assemblages in the surface ocean for which little genomic information is currently available. Bioinformatic techniques were used to assemble two nearly complete genomes from marine metagenomes and single-cell sequencing provided two more partial genomes. Recruitment of metagenomic data shows that these SAR86 genomes substantially increase our knowledge of non-photosynthetic bacteria in the surface ocean. Phylogenomic analyses establish SAR86 as a basal and divergent lineage of γ-proteobacteria, and the individual genomes display a temperature-dependent distribution. Modestly sized at 1.25-1.7 Mbp, the SAR86 genomes lack several pathways for amino-acid and vitamin synthesis as well as sulfate reduction, trends commonly observed in other abundant marine microbes. SAR86 appears to be an aerobic chemoheterotroph with the potential for proteorhodopsin-based ATP generation, though the apparent lack of a retinal biosynthesis pathway may require it to scavenge exogenously-derived pigments to utilize proteorhodopsin. The genomes contain an expanded capacity for the degradation of lipids and carbohydrates acquired using a wealth of tonB-dependent outer membrane receptors. Like the abundant planktonic marine bacterial clade SAR11, SAR86 exhibits metabolic streamlining, but also a distinct carbon compound specialization, possibly avoiding competition.

Genome of the Pathogen Porphyromonas Gingivalis Recovered from a Biofilm in a Hospital Sink Using a High-throughput Single-cell Genomics Platform

Genome Research. May, 2013  |  Pubmed ID: 23564253

Although biofilms have been shown to be reservoirs of pathogens, our knowledge of the microbial diversity in biofilms within critical areas, such as health care facilities, is limited. Available methods for pathogen identification and strain typing have some inherent restrictions. In particular, culturing will yield only a fraction of the species present, PCR of virulence or marker genes is mainly focused on a handful of known species, and shotgun metagenomics is limited in the ability to detect strain variations. In this study, we present a single-cell genome sequencing approach to address these limitations and demonstrate it by specifically targeting bacterial cells within a complex biofilm from a hospital bathroom sink drain. A newly developed, automated platform was used to generate genomic DNA by the multiple displacement amplification (MDA) technique from hundreds of single cells in parallel. MDA reactions were screened and classified by 16S rRNA gene PCR sequence, which revealed a broad range of bacteria covering 25 different genera representing environmental species, human commensals, and opportunistic human pathogens. Here we focus on the recovery of a nearly complete genome representing a novel strain of the periodontal pathogen Porphyromonas gingivalis (P. gingivalis JCVI SC001) using the single-cell assembly tool SPAdes. Single-cell genomics is becoming an accepted method to capture novel genomes, primarily in the marine and soil environments. Here we show for the first time that it also enables comparative genomic analysis of strain variation in a pathogen captured from complex biofilm samples in a healthcare facility.

Nearly Finished Genomes Produced Using Gel Microdroplet Culturing Reveal Substantial Intraspecies Genomic Diversity Within the Human Microbiome

Genome Research. May, 2013  |  Pubmed ID: 23493677

The majority of microbial genomic diversity remains unexplored. This is largely due to our inability to culture most microorganisms in isolation, which is a prerequisite for traditional genome sequencing. Single-cell sequencing has allowed researchers to circumvent this limitation. DNA is amplified directly from a single cell using the whole-genome amplification technique of multiple displacement amplification (MDA). However, MDA from a single chromosome copy suffers from amplification bias and a large loss of specificity from even very small amounts of DNA contamination, which makes assembling a genome difficult and completely finishing a genome impossible except in extraordinary circumstances. Gel microdrop cultivation allows culturing of a diverse microbial community and provides hundreds to thousands of genetically identical cells as input for an MDA reaction. We demonstrate the utility of this approach by comparing sequencing results of gel microdroplets and single cells following MDA. Bias is reduced in the MDA reaction and genome sequencing, and assembly is greatly improved when using gel microdroplets. We acquired multiple near-complete genomes for two bacterial species from human oral and stool microbiome samples. A significant amount of genome diversity, including single nucleotide polymorphisms and genome recombination, is discovered. Gel microdroplets offer a powerful and high-throughput technology for assembling whole genomes from complex samples and for probing the pan-genome of naturally occurring populations.

Single-cell Sequencing in Its Prime

Nature Biotechnology. Mar, 2013  |  Pubmed ID: 23471069

Sequencing of Isolated Sperm Cells for Direct Haplotyping of a Human Genome

Genome Research. May, 2013  |  Pubmed ID: 23282328

There is increasing evidence that the phenotypic effects of genomic sequence variants are best understood in terms of variant haplotypes rather than as isolated polymorphisms. Haplotype analysis is also critically important for uncovering population histories and for the study of evolutionary genetics. Although the sequencing of individual human genomes to reveal personal collections of sequence variants is now well established, there has been slower progress in the phasing of these variants into pairs of haplotypes along each pair of chromosomes. Here, we have developed a distinct approach to haplotyping that can yield chromosome-length haplotypes, including the vast majority of heterozygous single-nucleotide polymorphisms (SNPs) in an individual human genome. This approach exploits the haploid nature of sperm cells and employs a combination of genotyping and low-coverage sequencing on a short-read platform. In addition to generating chromosome-length haplotypes, the approach can directly identify recombination events (averaging 1.1 per chromosome) with a median resolution of <100 kb.

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