Microdiversity and temporal dynamics of marine bacterial dimethylsulfoniopropionate genes.

Dimethylsulfoniopropionate (DMSP) is an abundant organic sulfur metabolite produced by many phytoplankton species and degraded by bacteria via two distinct pathways with climate-relevant implications. We assessed the diversity and abundance of bacteria possessing these pathways in the context of phytoplankton community composition over a 3-week time period spanning September-October, 2014 in Monterey Bay, CA. The dmdA gene from the DMSP demethylation pathway dominated the DMSP gene pool and was harboured mostly by members of the alphaproteobacterial SAR11 clade and secondarily by the Roseobacter group, particularly during the second half of the study. Novel members of the DMSP-degrading community emerged from dmdA sequences recovered from metagenome assemblies and single-cell sequencing, including largely uncharacterized gammaproteobacteria and alphaproteobacteria taxa. In the DMSP cleavage pathway, the SAR11 gene dddK was the most abundant early in the study, but was supplanted by dddP over time. SAR11 members, especially those harbouring genes for both DMSP degradation pathways, had a strong positive relationship with the abundance of dinoflagellates, and DMSP-degrading gammaproteobacteria co-occurred with haptophytes. This in situ study of the drivers of DMSP fate in a coastal ecosystem demonstrates for the first time correlations between specific groups of bacterial DMSP degraders and phytoplankton taxa.

Ecological divergence of syntopic marine bacterial species is shaped by gene content and expression.

Identifying mechanisms by which bacterial species evolve and maintain genomic diversity is particularly challenging for the uncultured lineages that dominate the surface ocean. A longitudinal analysis of bacterial genes, genomes, and transcripts during a coastal phytoplankton bloom revealed two co-occurring, highly related Rhodobacteraceae species from the deeply branching and uncultured NAC11-7 lineage. These have identical 16S rRNA gene amplicon sequences, yet their genome contents assembled from metagenomes and single cells indicate species-level divergence. Moreover, shifts in relative dominance of the species during dynamic bloom conditions over 7 weeks confirmed the syntopic species' divergent responses to the same microenvironment at the same time. Genes unique to each species and genes shared but divergent in per-cell inventories of mRNAs accounted for 5% of the species' pangenome content. These analyses uncover physiological and ecological features that differentiate the species, including capacities for organic carbon utilization, attributes of the cell surface, metal requirements, and vitamin biosynthesis. Such insights into the coexistence of highly related and ecologically similar bacterial species in their shared natural habitat are rare.

Analysis of a viral metagenomic library from 200 m depth in Monterey Bay, California constructed by direct shotgun cloning.

BACKGROUND: Viruses have a profound influence on both the ecology and evolution of marine plankton, but the genetic diversity of viral assemblages, particularly those in deeper ocean waters, remains poorly described. Here we report on the construction and analysis of a viral metagenome prepared from below the euphotic zone in a temperate, eutrophic bay of coastal California. METHODS: We purified viruses from approximately one cubic meter of seawater collected from 200 m depth in Monterey Bay, CA. DNA was extracted from the virus fraction, sheared, and cloned with no prior amplification into a plasmid vector and propagated in E. coli to produce the MBv200m library. Random clones were sequenced by the Sanger method. Sequences were assembled then compared to sequences in GenBank and to other viral metagenomic libraries using BLAST analyses. RESULTS: Only 26% of the 881 sequences remaining after assembly had significant (E≤0.001) BLAST hits to sequences in the GenBank nr database, with most being matches to bacteria (15%) and viruses (8%). When BLAST analysis included environmental sequences, 74% of sequences in the MBv200m library had a significant match. Most of these hits (70%) were to microbial metagenome sequences and only 0.7% were to sequences from viral metagenomes. Of the 121 sequences with a significant hit to a known virus, 94% matched bacteriophages (Families Podo-, Sipho-, and Myoviridae) and 6% matched viruses of eukaryotes in the Family Phycodnaviridae (5 sequences) or the Mimivirus (2 sequences). The largest percentages of hits to viral genes of known function were to those involved in DNA modification (25%) or structural genes (17%). Based on reciprocal BLAST analyses, the MBv200m library appeared to be most similar to viral metagenomes from two other bays and least similar to a viral metagenome from the Arctic Ocean. CONCLUSIONS: Direct cloning of DNA from diverse marine viruses was feasible and resulted in a distribution of virus types and functional genes at depth that differed in detail, but were broadly similar to those found in surface marine waters. Targeted viral analyses are useful for identifying those components of the greater marine metagenome that circulate in the subcellular size fraction.

A system of coordinated autonomous robots for Lagrangian studies of microbes in the oceanic deep chlorophyll maximum.

The deep chlorophyll maximum (DCM) layer is an ecologically important feature of the open ocean. The DCM cannot be observed using aerial or satellite remote sensing; thus, in situ observations are essential. Further, understanding the responses of microbes to the environmental processes driving their metabolism and interactions requires observing in a reference frame that moves with a plankton population drifting in ocean currents, i.e., Lagrangian. Here, we report the development and application of a system of coordinated robots for studying planktonic biological communities drifting within the ocean. The presented Lagrangian system uses three coordinated autonomous robotic platforms. The focal platform consists of an autonomous underwater vehicle (AUV) fitted with a robotic water sampler. This platform localizes and drifts within a DCM community, periodically acquiring samples while continuously monitoring the local environment. The second platform is an AUV equipped with environmental sensing and acoustic tracking capabilities. This platform characterizes environmental conditions by tracking the focal platform and vertically profiling in its vicinity. The third platform is an autonomous surface vehicle equipped with satellite communications and subsea acoustic tracking capabilities. While also acoustically tracking the focal platform, this vehicle serves as a communication relay that connects the subsea robot to human operators, thereby providing situational awareness and enabling intervention if needed. Deployed in the North Pacific Ocean within the core of a cyclonic eddy, this coordinated system autonomously captured fundamental characteristics of the in situ DCM microbial community in a manner not possible previously.

Remote, autonomous real-time monitoring of environmental DNA from commercial fish.

Environmental DNA (eDNA) is increasingly used for monitoring marine organisms; however, offshore sampling and time lag from sampling to results remain problematic. In order to overcome these challenges a robotic sampler, a 2nd generation Environmental Sample Processor (ESP), was tested for autonomous analysis of eDNA from four commercial fish species in a 4.5 million liter mesocosm. The ESP enabled in situ analysis, consisting of water collection, filtration, DNA extraction and qPCR analysis, which allowed for real-time remote reporting and archival sample collection, consisting of water collection, filtration and chemical preservation followed by post-deployment laboratory analysis. The results demonstrate that the 2G ESP was able to consistently detect and quantify target molecules from the most abundant species (Atlantic mackerel) both in real-time and from the archived samples. In contrast, detection of low abundant species was challenged by both biological and technical aspects coupled to the ecology of eDNA and the 2G ESP instrumentation. Comparison of the in situ analysis and archival samples demonstrated variance, which potentially was linked to diel migration patterns of the Atlantic mackerel. The study demonstrates strong potential for remote autonomous in situ monitoring which open new possibilities for the field of eDNA and marine monitoring.

Near real-time, autonomous detection of marine bacterioplankton on a coastal mooring in Monterey Bay, California, using rRNA-targeted DNA probes.

A sandwich hybridization assay (SHA) was developed to detect 16S rRNAs indicative of phylogenetically distinct groups of marine bacterioplankton in a 96-well plate format as well as low-density arrays printed on a membrane support. The arrays were used in a field-deployable instrument, the Environmental Sample Processor (ESP). The SHA employs a chaotropic buffer for both cell homogenization and hybridization, thus target sequences are captured directly from crude homogenates. Capture probes for seven of nine different bacterioplankton clades examined reacted specifically when challenged with target and non-target 16S rRNAs derived from in vitro transcribed 16S rRNA genes cloned from natural samples. Detection limits were between 0.10-1.98 and 4.43- 12.54 fmole ml(-1) homogenate for the 96-well plate and array SHA respectively. Arrays printed with five of the bacterioplankton-specific capture probes were deployed on the ESP in Monterey Bay, CA, twice in 2006 for a total of 25 days and also utilized in a laboratory time series study. Groups detected included marine alphaproteobacteria, SAR11, marine cyanobacteria, marine group I crenarchaea, and marine group II euryarchaea. To our knowledge this represents the first report of remote in situ DNA probe-based detection of marine bacterioplankton.

Pathways of carbon assimilation and ammonia oxidation suggested by environmental genomic analyses of marine Crenarchaeota.

Marine Crenarchaeota represent an abundant component of oceanic microbiota with potential to significantly influence biogeochemical cycling in marine ecosystems. Prior studies using specific archaeal lipid biomarkers and isotopic analyses indicated that planktonic Crenarchaeota have the capacity for autotrophic growth, and more recent cultivation studies support an ammonia-based chemolithoautotrophic energy metabolism. We report here analysis of fosmid sequences derived from the uncultivated marine crenarchaeote, Cenarchaeum symbiosum, focused on the reconstruction of carbon and energy metabolism. Genes predicted to encode multiple components of a modified 3-hydroxypropionate cycle of autotrophic carbon assimilation were identified, consistent with utilization of carbon dioxide as a carbon source. Additionally, genes predicted to encode a near complete oxidative tricarboxylic acid cycle were also identified, consistent with the consumption of organic carbon and in the production of intermediates for amino acid and cofactor biosynthesis. Therefore, C. symbiosum has the potential to function either as a strict autotroph, or as a mixotroph utilizing both carbon dioxide and organic material as carbon sources. From the standpoint of energy metabolism, genes predicted to encode ammonia monooxygenase subunits, ammonia permease, urease, and urea transporters were identified, consistent with the use of reduced nitrogen compounds as energy sources fueling autotrophic metabolism. Homologues of these genes, recovered from ocean waters worldwide, demonstrate the conservation and ubiquity of crenarchaeal pathways for carbon assimilation and ammonia oxidation. These findings further substantiate the likely global metabolic importance of Crenarchaeota with respect to key steps in the biogeochemical transformation of carbon and nitrogen in marine ecosystems.

Microbial metagenomes and metatranscriptomes during a coastal phytoplankton bloom.

Metagenomic and metatranscriptomic time-series data covering a 52-day period in the fall of 2016 provide an inventory of bacterial and archaeal community genes, transcripts, and taxonomy during an intense dinoflagellate bloom in Monterey Bay, CA, USA. The dataset comprises 84 metagenomes (0.8 terabases), 82 metatranscriptomes (1.1 terabases), and 88 16S rRNA amplicon libraries from samples collected on 41 dates. The dataset also includes 88 18S rRNA amplicon libraries, characterizing the taxonomy of the eukaryotic community during the bloom. Accompanying the sequence data are chemical and biological measurements associated with each sample. These datasets will facilitate studies of the structure and function of marine bacterial communities during episodic phytoplankton blooms.

Single-taxon field measurements of bacterial gene regulation controlling DMSP fate.

The 'bacterial switch' is a proposed regulatory point in the global sulfur cycle that routes dimethylsulfoniopropionate (DMSP) to two fundamentally different fates in seawater through genes encoding either the cleavage or demethylation pathway, and affects the flux of volatile sulfur from ocean surface waters to the atmosphere. Yet which ecological or physiological factors might control the bacterial switch remains a topic of considerable debate. Here we report the first field observations of dynamic changes in expression of DMSP pathway genes by a single marine bacterial species in its natural environment. Detection of taxon-specific gene expression in Roseobacter species HTCC2255 during a month-long deployment of an autonomous ocean sensor in Monterey Bay, CA captured in situ regulation of the first gene in each DMSP pathway (dddP and dmdA) that corresponded with shifts in the taxonomy of the phytoplankton community. Expression of the demethylation pathway was relatively greater during a high-DMSP-producing dinoflagellate bloom, and expression of the cleavage pathway was greater in the presence of a mixed diatom and dinoflagellate community [corrected].These field data fit the prevailing hypothesis for bacterial DMSP gene regulation based on bacterial sulfur demand, but also suggest a modification involving oxidative stress response, evidenced as upregulation of catalase via katG, when DMSP is demethylated.

Quantitative PCR method for enumeration of cells of cryptic species of the toxic marine dinoflagellate Ostreopsis spp. in coastal waters of Japan.

Monitoring of harmful algal bloom (HAB) species in coastal waters is important for assessment of environmental impacts associated with HABs. Co-occurrence of multiple cryptic species such as toxic dinoflagellate Ostreopsis species make reliable microscopic identification difficult, so the employment of molecular tools is often necessary. Here we developed new qPCR method by which cells of cryptic species can be enumerated based on actual gene number of target species. The qPCR assay targets the LSU rDNA of Ostreopsis spp. from Japan. First, we constructed standard curves with a linearized plasmid containing the target rDNA. We then determined the number of rDNA copies per cell of target species from a single cell isolated from environmental samples using the qPCR assay. Differences in the DNA recovery efficiency was calculated by adding exogenous plasmid to a portion of the sample lysate before and after DNA extraction followed by qPCR. Then, the number of cells of each species was calculated by division of the total number of rDNA copies of each species in the samples by the number of rDNA copies per cell. To test our procedure, we determined the total number of rDNA copies using environmental samples containing no target cells but spiked with cultured cells of several species of Ostreopsis. The numbers estimated by the qPCR method closely approximated total numbers of cells added. Finally, the numbers of cells of target species in environmental samples containing cryptic species were enumerated by the qPCR method and the total numbers also closely approximated the microscopy cell counts. We developed a qPCR method that provides accurate enumeration of each cryptic species in environments. This method is expected to be a powerful tool for monitoring the various HAB species that occur as cryptic species in coastal waters.

Seasonal Synechococcus and Thaumarchaeal population dynamics examined with high resolution with remote in situ instrumentation.

Monterey Bay, CA is an Eastern boundary upwelling system that is nitrogen limited much of the year. In order to resolve population dynamics of microorganisms important for nutrient cycling in this region, we deployed the Environmental Sample Processor with quantitative PCR assays targeting both ribosomal RNA genes and functional genes for subclades of cyanobacteria (Synechococcus) and ammonia-oxidizing Archaea (Thaumarchaeota) populations. Results showed a strong correlation between Thaumarchaea abundances and nitrate during the spring upwelling but not the fall sampling period. In relatively stratified fall waters, the Thaumarchaeota community reached higher numbers than in the spring, and an unexpected positive correlation with chlorophyll concentration was observed. Further, we detected drops in Synechococcus abundance that occurred on short (that is, daily) time scales. Upwelling intensity and blooms of eukaryotic phytoplankton strongly influenced Synechococcus distributions in the spring and fall, revealing what appear to be the environmental limitations of Synechococcus populations in this region. Each of these findings has implications for Monterey Bay biogeochemistry. High-resolution sampling provides a better-resolved framework within which to observe changes in the plankton community. We conclude that controls on these ecosystems change on smaller scales than are routinely assessed, and that more predictable trends will be uncovered if they are evaluated within seasonal (monthly), rather than on annual or interannual scales.

Metatranscriptomic analysis of autonomously collected and preserved marine bacterioplankton.

Planktonic microbial activity and community structure is dynamic, and can change dramatically on time scales of hours to days. Yet for logistical reasons, this temporal scale is typically under-sampled in the marine environment. In order to facilitate higher-resolution, long-term observation of microbial diversity and activity, we developed a protocol for automated collection and fixation of marine microbes using the Environmental Sample Processor (ESP) platform. The protocol applies a preservative (RNALater) to cells collected on filters, for long-term storage and preservation of total cellular RNA. Microbial samples preserved using this protocol yielded high-quality RNA after 30 days of storage at room temperature, or onboard the ESP at in situ temperatures. Pyrosequencing of complementary DNA libraries generated from ESP-collected and preserved samples yielded transcript abundance profiles nearly indistinguishable from those derived from conventionally treated replicate samples. To demonstrate the utility of the method, we used a moored ESP to remotely and autonomously collect Monterey Bay seawater for metatranscriptomic analysis. Community RNA was extracted and pyrosequenced from samples collected at four time points over the course of a single day. In all four samples, the oxygenic photoautotrophs were predominantly eukaryotic, while the bacterial community was dominated by Polaribacter-like Flavobacteria and a Rhodobacterales bacterium sharing high similarity with Rhodobacterales sp. HTCC2255. However, each time point was associated with distinct species abundance and gene transcript profiles. These laboratory and field tests confirmed that autonomous collection and preservation is a feasible and useful approach for characterizing the expressed genes and environmental responses of marine microbial communities.

Underwater application of quantitative PCR on an ocean mooring.

The Environmental Sample Processor (ESP) is a device that allows for the underwater, autonomous application of DNA and protein probe array technologies as a means to remotely identify and quantify, in situ, marine microorganisms and substances they produce. Here, we added functionality to the ESP through the development and incorporation of a module capable of solid-phase nucleic acid extraction and quantitative PCR (qPCR). Samples collected by the instrument were homogenized in a chaotropic buffer compatible with direct detection of ribosomal RNA (rRNA) and nucleic acid purification. From a single sample, both an rRNA community profile and select gene abundances were ascertained. To illustrate this functionality, we focused on bacterioplankton commonly found along the central coast of California and that are known to vary in accordance with different oceanic conditions. DNA probe arrays targeting rRNA revealed the presence of 16S rRNA indicative of marine crenarchaea, SAR11 and marine cyanobacteria; in parallel, qPCR was used to detect 16S rRNA genes from the former two groups and the large subunit RuBisCo gene (rbcL) from Synecchococcus. The PCR-enabled ESP was deployed on a coastal mooring in Monterey Bay for 28 days during the spring-summer upwelling season. The distributions of the targeted bacterioplankon groups were as expected, with the exception of an increase in abundance of marine crenarchaea in anomalous nitrate-rich, low-salinity waters. The unexpected co-occurrence demonstrated the utility of the ESP in detecting novel events relative to previously described distributions of particular bacterioplankton groups. The ESP can easily be configured to detect and enumerate genes and gene products from a wide range of organisms. This study demonstrated for the first time that gene abundances could be assessed autonomously, underwater in near real-time and referenced against prevailing chemical, physical and bulk biological conditions.

Potential for chemolithoautotrophy among ubiquitous bacteria lineages in the dark ocean.

Recent studies suggest that unidentified prokaryotes fix inorganic carbon at globally significant rates in the immense dark ocean. Using single-cell sorting and whole-genome amplification of prokaryotes from two subtropical gyres, we obtained genomic DNA from 738 cells representing most cosmopolitan lineages. Multiple cells of Deltaproteobacteria cluster SAR324, Gammaproteobacteria clusters ARCTIC96BD-19 and Agg47, and some Oceanospirillales from the lower mesopelagic contained ribulose-1,5-bisphosphate carboxylase-oxygenase and sulfur oxidation genes. These results corroborated community DNA and RNA profiling from diverse geographic regions. The SAR324 genomes also suggested C(1) metabolism and a particle-associated life-style. Microautoradiography and fluorescence in situ hybridization confirmed bicarbonate uptake and particle association of SAR324 cells. Our study suggests potential chemolithoautotrophy in several uncultured Proteobacteria lineages that are ubiquitous in the dark oxygenated ocean and provides new perspective on carbon cycling in the ocean's largest habitat.

A robotic molecular method for in situ detection of marine invertebrate larvae.

Knowledge of the temporal and spatial abundance of invertebrate larvae is critical to understanding the dispersal capabilities and recruitment potential of marine and aquatic organisms. Traditional microscopic analyses are time-consuming and difficult given the diversity of larval species and a frequent lack of discriminating morphological characteristics. Here, we describe a sensitive rRNA targeted sandwich hybridization assay (SHA) that uses oligonucleotide probes to detect and enumerate the larvae of invasive green crabs (Carcinus maenas), native blue mussels (Mytilus), native barnacles (Balanus) and polychaetes (Osedax and Ophelia) that occur in the Monterey Bay National Marine Sanctuary, California. Laboratory-based assays demonstrate specificity, high sensitivity, and a quantitative response to cultured samples from three of the target organisms. Oligonucleotide probes were then printed in arrays on nitrocellulose membranes and deployed in our robotic Environmental Sample Processor (ESP) to detect larvae in situ and autonomously. We demonstrate that the SHA-detection method and ESP robot can be used for near real-time, in situ detection of larval species in the marine environment.

Community genomics among stratified microbial assemblages in the ocean's interior.

Microbial life predominates in the ocean, yet little is known about its genomic variability, especially along the depth continuum. We report here genomic analyses of planktonic microbial communities in the North Pacific Subtropical Gyre, from the ocean's surface to near-sea floor depths. Sequence variation in microbial community genes reflected vertical zonation of taxonomic groups, functional gene repertoires, and metabolic potential. The distributional patterns of microbial genes suggested depth-variable community trends in carbon and energy metabolism, attachment and motility, gene mobility, and host-viral interactions. Comparative genomic analyses of stratified microbial communities have the potential to provide significant insight into higher-order community organization and dynamics.

Comparison of fluorescently labeled oligonucleotide and polynucleotide probes for the detection of pelagic marine bacteria and archaea.

We compared the detection of bacteria and archaea in the coastal North Sea and at Monterey Bay, Calif., after fluorescence in situ hybridization (FISH) either with rRNA-targeted oligonucleotide probes monolabeled with the cyanin dye Cy3 (oligoFISH) or with fluorescein-labeled polyribonucleotide probes (polyFISH). During an annual cycle in German Bight surface waters, the percentages of bacteria visualized by polyFISH (annual mean, 77% of total counts) were significantly higher than those detected by oligoFISH (53%). The fraction of total bacteria visualized by oligoFISH declined during winter, whereas cell numbers determined by polyFISH remained constant throughout the year. Depth profiles from Monterey Bay showed large differences in the fraction of bacterial cells visualized by polyFISH and oligoFISH in the deeper water layers irrespective of the season. Image-analyzed microscopy indicated that the superior detection of cells by polyFISH with fluorescein-labeled probes in bacterioplankton samples was less a consequence of higher absolute fluorescence intensities but was rather related to quasi-linear bleaching dynamics and to a higher signal-to-background ratio. The relative abundances of archaea in North Sea and Monterey Bay spring samples as determined by oligoFISH were on average higher than those determined by polyFISH. However, simultaneous hybridizations with oligonucleotide probes for bacteria and archaea suggested that the oligoFISH probe ARCH915 unspecifically stained a population of bacteria. Using either FISH technique, blooms of archaea were observed in North Sea surface waters during the spring and summer months. Marine group II archaea (Euryarchaeota) reached >30% of total picoplankton abundances, as determined by polyFISH. We suggest that studies of pelagic microbial community structure using oligoFISH with monolabeled probes should focus on environments that yield detections > or =70% of total cell counts, e.g., coastal surface waters during spring and summer.

Different SAR86 subgroups harbour divergent proteorhodopsins.

Proteorhodopsins (PRs), bacterial photoactive proton pumps, were originally detected in the uncultured marine gamma-proteobacterial SAR86 group. PRs are now known to occur in both the gamma and alpha marine proteobacterial lineages. Recent environmental shotgun sequence analysis in the Sargasso Sea has added yet more diversity, and a potentially broader taxonomic distribution, to the PR family. Much remains to be learned, however, about within-taxon PR variability and the broader organismal distribution of different PR types. We report here genomic analyses of large genome fragments from different subgroups of the SAR86 lineage, recovered from naturally occurring bacterioplankton populations in coastal Red Sea and open ocean Pacific waters. Sequence comparisons were performed on large bacterial artificial chromosomes (BACs) bearing both rRNA and PR genes, derived from different SAR86 subgroups. Our analyses indicated the presence of different PR sequence types within the same SAR86 rRNA subgroup. The data suggested that the distribution of particular PR types does not necessarily parallel the phylogenetic relationship inferred from highly conserved genes such as rRNA. Further analyses of the genomic regions flanking PR also revealed a potential pathway for the biosynthesis of retinal, the PR chromophore that is required to generate the functionally active photoprotein. Finally, comparison of our results with recently reported Sargasso Sea environmental shotgun sequence assemblies demonstrated the utility of BAC clones for interpreting environmental shotgun sequence data, much of which is represented in short contigs that have an overall low depth of coverage.

Identification of methyl coenzyme M reductase A (mcrA) genes associated with methane-oxidizing archaea.

Phylogenetic and stable-isotope analyses implicated two methanogen-like archaeal groups, ANME-1 and ANME-2, as key participants in the process of anaerobic methane oxidation. Although nothing is known about anaerobic methane oxidation at the molecular level, the evolutionary relationship between methane-oxidizing archaea (MOA) and methanogenic archaea raises the possibility that MOA have co-opted key elements of the methanogenic pathway, reversing many of its steps to oxidize methane anaerobically. In order to explore this hypothesis, the existence and genomic conservation of methyl coenzyme M reductase (MCR), the enzyme catalyzing the terminal step in methanogenesis, was studied in ANME-1 and ANME-2 archaea isolated from various marine environments. Clone libraries targeting a conserved region of the alpha subunit of MCR (mcrA) were generated and compared from environmental samples, laboratory-incubated microcosms, and fosmid libraries. Four out of five novel mcrA types identified from these sources were associated with ANME-1 or ANME-2 group members. Assignment of mcrA types to specific phylogenetic groups was based on environmental clone recoveries, selective enrichment of specific MOA and mcrA types in a microcosm, phylogenetic congruence between mcrA and small-subunit rRNA tree topologies, and genomic context derived from fosmid sequences. Analysis of the ANME-1 and ANME-2 mcrA sequences suggested the potential for catalytic activity based on conservation of active-site amino acids. These results provide a basis for identifying methanotrophic archaea with mcrA sequences and define a functional genomic link between methanogenic and methanotrophic archaea.