Biology subjects

Banfield, J. F.

Publications and source records attributed to Banfield, J. F..

At least 73 records · Page 4Linked to original sources

bioRxiv2019

Accurate and Complete Genomes from Metagenomes

Genomes are an integral component of the biological information about an organism and, logically, the more complete the genome, the more informative it is. Historically, bacterial and archaeal genomes were reconstructed from pure (monoclonal) cultures and the first reported sequences were manually curated to completion. However, the bottleneck imposed by the requirement for isolates precluded genomic insights for the vast majority of microbial life. Shotgun sequencing of microbial communities, referred to initially as community genomics and subsequently as genome-resolved metagenomics, can circumvent this limitation by obtaining metagenome-assembled genomes (MAGs), but gaps, local assembly errors, chimeras and contamination by fragments from other genomes limit the value of these genomes. Here, we discuss genome curation to improve and in some cases achieve complete (circularized, no gaps) MAGs (CMAGs). To date, few CMAGs have been generated, although notably some are from very complex systems such as soil and sediment. Through analysis of ~7000 published complete bacterial isolate genomes, we verify the value of cumulative GC skew in combination with other metrics to establish bacterial genome sequence accuracy. Interestingly, analysis of cumulative GC skew identified potential mis-assemblies in some reference genomes of isolated bacteria and the repeat sequences that likely gave rise to them. We discuss methods that could be implemented in bioinformatic approaches for curation to ensure that metabolic and evolutionary analyses can be based on very high-quality genomes.

microbiology↗

bioRxiv2019

Taxonomically and metabolically distinct microbial communities with depth and across a hillslope to riparian zone transect

Watersheds are important for supplying fresh water, the quality of which depends on complex interplay involving physical, chemical and biological processes. As water percolates through the soil and underlying weathering rock en route to the river corridor, microorganisms mediate key geochemical transformations, yet the distribution and functional capacities of subsurface microbial communities remain little understood. We have studied metabolic capacities of microbial communities along a meadow to floodplain hillslope transect within the East-River watershed, Colorado, using genome resolved metagenomics and carbon and hydrogen stable isotopes. Very limited strain/species overlap was found at different depths below the ground surface and at different distances along the hillslope, possibly due to restricted hydraulic connectivity after early stages of snowmelt. Functions such as carbon fixation and selenate reduction were prevalent at multiple sites, although the lineages of organisms responsible tend to be location-specific. Based on its abundance, sulfur is significantly more important for microbial metabolism at the floodplain compared to on the hillslope. Nitrification and methylamine oxidation are likely only occurring within the floodplain, with nitrification capacity in shallow soil, and methylamine oxidation in deeper unsaturated sediment. Biogenic methane was detected in deep surface samples, but methanogenic organisms were not identified. Originality-Significance StatementIn a previous study within a hillslope to riparian zone transect of a sub-alpine watershed, the community structure was explored using ribosomal protein S3 genes, and the metabolic potential was hypothesized based on the presence of metabolism related genes. However, tying specific strains and species to metabolic functioning was not discussed as resolved genomes were not available. In the current study, we use genome-resolved metagenomics along with carbon and hydrogen stable isotopes to explore the spatial distribution of biogeochemical processes. By linking taxonomy and function, using multiple functional genes indicative of full metabolic pathways, we detect heterogeneity in the distribution of metabolic potential and the organisms involved with depth and landscape position. Thus, we infer how microbiome genomic variation impacts biogeochemical cycling across the watershed. We found very limited strain/species overlap at different depths below the surface and along the hillslope, possibly due to the restricted site to site hydraulic connectivity, and show that communities are largely distinct in their metabolic capacities. Both proximity to the river and the underlying Mancos shale apparently control species distribution and metabolic potential. Functions such as carbon fixation and selenate reduction were prevalent at multiple sites, although the lineages of organisms responsible tend to be location-specific. Arsenate detoxification was found to be prevalent in the riparian zone whereas selenate reduction was detected within weathered Mancos shale. We conclude that important ecosystem functions are strongly associated with the riparian zone, some of which may have crucial implications as to water quality and human health.

bioinformatics↗

bioRxiv2019

Aquatic Elusimicrobia are metabolically diverse compared to gut microbiome Elusimicrobia and some have novel nitrogenase-like gene clusters

Currently described members of Elusimicrobia, a relatively recently defined phylum, are animal-associated and rely on fermentation. However, free-living Elusimicrobia have been detected in sediments, soils and groundwater, raising questions regarding their metabolic capacities and evolutionary relationship to animal-associated species. Here, we analyzed 94 draft-quality, non-redundant genomes, including 30 newly reconstructed genomes, from diverse animal-associated and natural environments. Genomes group into 12 clades, 10 of which previously lacked reference genomes. Groundwater-associated Elusimicrobia are predicted to be capable of heterotrophic or autotrophic lifestyles, reliant on oxygen or nitrate/nitrite-dependent respiration, or a variety of organic compounds and Rhodobacter nitrogen fixation-dependent (Rnf-dependent) acetogenesis with hydrogen and carbon dioxide as the substrates. Genomes from two clades of groundwater-associated Elusimicrobia often encode a new group of nitrogenase paralogs that co-occur with an extensive suite of radical S-Adenosylmethionine (SAM) proteins. We identified similar genomic loci in genomes of bacteria from the Gracilibacteria phylum and the Myxococcales order and predict that the gene clusters reduce a tetrapyrrole, possibly to form a novel cofactor. The animal-associated Elusimicrobia clades nest phylogenetically within two free-living-associated clades. Thus, we propose an evolutionary trajectory in which some Elusimicrobia adapted to animal-associated lifestyles from free-living species via genome reduction.

microbiology↗

bioRxiv2019

Soil bacterial populations are shaped by recombination and gene-specific selection across a meadow

Soil microbial diversity is often studied from the perspective of community composition, but less is known about genetic heterogeneity within species and how population structures are affected by dispersal, recombination, and selection. Genomic inferences about population structure can be made using the millions of sequencing reads that are assembled de novo into consensus genomes from metagenomes, as each read pair describes a short genomic sequence from a cell in the population. Here we track genome-wide population genetic variation for 19 highly abundant bacterial species sampled from across a grassland meadow. Genomic nucleotide identity of assembled genomes was significantly associated with local geography for half of the populations studied, and for a majority of populations within-sample nucleotide diversity could often be as high as meadow-wide nucleotide diversity. Genes involved in specialized metabolite biosynthesis and extracellular transport were characterized by elevated genetic diversity in multiple species. Microbial populations displayed varying degrees of homologous recombination and recombinant variants were often detected at 7-36% of loci genome-wide. Within multiple populations we identified genes with unusually high site-specific differentiation of alleles, fewer recombinant events, and lower nucleotide diversity, suggesting recent selective sweeps for gene variants. Taken together, these results indicate that recombination and gene-specific selection commonly shape local soil bacterial genetic variation.

microbiology↗

bioRxiv2019

Wide distribution of phage that infect freshwater SAR11 bacteria

Fonsibacter (LD12 subclade) are among the most abundant bacterioplankton in freshwater ecosystems. These bacteria belong to the order Pelagibacterales (SAR11) and are related to Pelagibacter (marine SAR11) that dominate many marine habitats. Although a handful of Pelagibacter phage (Pelagiphage) have been described, no phage that infect Fonsibacter have been reported. In this study, a complete Fonsibacter genome containing a prophage was reconstructed from metagenomic data. A circularized and complete genome related to the prophage, referred to as uv-Fonsiphage-EPL, shows high similarity to marine Pelagiphage HTVC025P. Additionally, we reconstructed three complete and one draft genome of phage related to marine Pelagiphage HTVC010P, and predicted a lytic strategy. The similarity in codon usage and co-occurrence patterns of HTVC010P-related phage and Fonsibacter suggested that these phage infect Fonsibacter. Similar phage were detected in Lake Mendota, Wisconsin, where Fonsibacter is also present. A search of related phage revealed the worldwide distribution of some genotypes in freshwater ecosystems, suggesting their substantial role in shaping indigenous microbial assemblages and influence on biogeochemical cycling. However, the uv-Fonsiphage-EPL and one lineage of HTVC010P-related phage have a more limited distribution in freshwater ecosystems. Based on this, and their close phylogenetic relatedness with Pelagiphage, we predict that they transitioned from saline into freshwater ecosystems comparatively recently. Overall, the findings provide insights into the genomic features of phage that infect Fonsibacter, and expand understanding of the ecology and evolution of these important bacteria.

microbiology↗

bioRxiv2019

Consistent metagenome-derived metrics verify and define bacterial species boundaries

Longstanding questions relate to the existence of naturally distinct bacterial species and genetic approaches to distinguish them. Bacterial genomes in public databases form distinct groups, but these databases are subject to isolation and deposition biases. We compared 5,203 bacterial genomes from 1,457 environmental metagenomic samples to test for distinct clouds of diversity, and evaluated metrics that could be used to define the species boundary. Bacterial genomes from the human gut, soil, and the ocean all exhibited gaps in whole-genome average nucleotide identities (ANI) near the previously suggested species threshold of 95% ANI. While genome-wide ratios of non-synonymous and synonymous nucleotide differences (dN/dS) decrease until ANI values approach [~]98%, estimates for homologous recombination approached zero at [~]95% ANI, supporting breakdown of recombination due to sequence divergence as a species-forming force. We evaluated 107 genome-based metrics for their ability to distinguish species when full genomes are not recovered. Full length 16S rRNA genes were least useful because they were under-recovered from metagenomes, but many ribosomal proteins displayed both high metagenomic recoverability and species-discrimination power. Taken together, our results verify the existence of sequence-discrete microbial species in metagenome-derived genomes and highlight the usefulness of ribosomal genes for gene-level species discrimination.

microbiology↗

bioRxiv2019

Niche differentiation is spatially and temporally regulated in the rhizosphere

The rhizosphere is a hotspot for microbial C transformations, and the origin of root polysaccharides and polymeric carbohydrates that are important precursors to soil organic matter. However, the ecological mechanisms that underpin rhizosphere carbohydrate depolymerization are poorly understood. Using Avena fatua, a common annual grass, we analyzed time-resolved metatranscriptomes to compare microbial function in rhizosphere, detritusphere, and combined rhizosphere-detritusphere habitats. Population transcripts were binned with a unique reference database generated from soil isolate and single amplified genomes, metagenomes, and stable isotope probing metagenomes. While soil habitat significantly affected both community composition and overall gene expression, succession of microbial functions occurred at a faster time scale than compositional changes. Using hierarchical clustering of upregulated decomposition gene expression, we identified four distinct microbial guilds populated by taxa whose functional succession patterns suggest specialization for substrates provided by fresh growing roots, decaying root detritus, the combination of live and decaying root biomass, or aging root material. Carbohydrate depolymerization genes were consistently upregulated in the rhizosphere, and both taxonomic and functional diversity were high in the combined rhizosphere-detritusphere--suggesting coexistence of rhizosphere guilds is facilitated by niche differentiation. Metatranscriptome-defined guilds provide a framework to model rhizosphere succession and its consequences for soil carbon cycling.

ecology↗

bioRxiv2019

Metatranscriptomic reconstruction reveals RNA viruses with the potential to shape carbon cycling in soil

Viruses impact nearly all organisms on Earth, with ripples of influence in agriculture, health and biogeochemical processes. However, very little is known about RNA viruses in an environmental context, and even less is known about their diversity and ecology in the most complex microbial system, soil. Here, we assembled 48 individual metatranscriptomes from four habitats within a soil sampled over a 22-day time series: rhizosphere alone, detritosphere alone, a combination of the two, and unamended soil (four time points and three biological replicates per time point). We resolved the RNA viral community, uncovering a high diversity of viral sequences. We also investigated possible host organisms by analyzing metatranscriptome marker gene content. Based on viral phylogeny, much of the diversity was Narnaviridae that parasitize fungi or Leviviridae that infect Proteobacteria. Both host and viral communities appear to be highly dynamic, and rapidly diverged depending on experimental conditions. The viral communities were structured based on the presence of litter, while putative hosts appeared to be impacted by both the presence of litter and roots. A clear time signature from Leviviridae and their hosts indicated that viruses were replicating. With this time-resolved analysis, we show that RNA viruses are diverse, abundant and active in soil. Their replication causes host cell death, mobilizing carbon in a process that represents a largely overlooked component of carbon cycling in soil.

microbiology↗

bioRxiv2019

Unusual metabolism and hypervariation in the genome of a Gracilibacteria (BD1-5) from an oil degrading community

The Candidate Phyla Radiation (CPR) comprises a large monophyletic group of bacterial lineages known almost exclusively based on genomes obtained using cultivation-independent methods. Within the CPR, Gracilibacteria (BD1-5) are particularly poorly understood due to undersampling and the inherent fragmented nature of available genomes. Here, we report the first closed, curated genome of a Gracilibacteria from an enrichment experiment inoculated from the Gulf of Mexico and designed to investigate hydrocarbon degradation. The gracilibacterium rose in abundance after the community switched to dominance by Colwellia. Notably, we predict that this gracilibacterium completely lacks glycolysis, the pentose phosphate and Entner-Doudoroff pathways. It appears to acquire pyruvate, acetyl-CoA and oxaloacetate via degradation of externally derived citrate, malate and amino acids and may use compound interconversion and oxidoreductases to generate and recycle reductive power. The initial genome assembly was fragmented in an unusual gene that is hypervariable within a repeat region. Such extreme local variation is rare, but characteristic of genes that confer traits under pressure to diversify within a population. Notably, the four major repeated 9-mer nucleotide sequences all generate a proline-threonine-aspartic acid (PTD) repeat. The genome of an abundant Colwellia psychrerythraea population has a large extracellular protein that also contains the repeated PTD motif. Although we do not know the host for the BD1-5 cell, the high relative abundance of the C. psychrerythraea population and the shared surface protein repeat may indicate an association between these bacteria.\n\nImportanceCPR bacteria are generally predicted to be symbionts due to their extensive biosynthetic deficits. Although monophyletic, they are not monolithic in terms of their lifestyles. The organism described here appears to have evolved an unusual metabolic platform not reliant on glucose or pentose sugars. Its biology appears to be centered around bacterial host-derived compounds and/or cell detritus. Amino acids likely provide building blocks for nucleic acids, peptidoglycan and protein synthesis. We resolved an unusual repeat region that would be invisible without genome curation. The nucleotide sequence is apparently under strong diversifying selection but the amino acid sequence is under stabilizing selection. The amino acid repeat also occurs in a surface protein of a coexisting bacterium, suggesting co-location and possibly interdependence.

microbiology↗

bioRxiv2019

Clades of huge phage from across Earth’s ecosystems

Phage typically have small genomes and depend on their bacterial hosts for replication. DNA sequenced from many diverse ecosystems revealed hundreds of huge phage genomes, between 200 kbp and 716 kbp in length. Thirty-four genomes were manually curated to completion, including the largest phage genomes yet reported. Expanded genetic repertoires include diverse and new CRISPR-Cas systems, tRNAs, tRNA synthetases, tRNA modification enzymes, translation initiation and elongation factors, and ribosomal proteins. Phage CRISPR-Cas systems have the capacity to silence host transcription factors and translational genes, potentially as part of a larger interaction network that intercepts translation to redirect biosynthesis to phage-encoded functions. In addition, some phage may repurpose bacterial CRISPR-Cas systems to eliminate competing phage. We phylogenetically define major clades of huge phage from human and other animal microbiomes, oceans, lakes, sediments, soils and the built environment. We conclude that their large gene inventories reflect a conserved biological strategy, observed over a broad bacterial host range and across Earths ecosystems.

microbiology↗

bioRxiv2019

Necrotizing enterocolitis is preceded by increased gut bacterial replication, Klebsiella, and fimbriae-encoding bacteria that may stimulate TLR4 receptors

Necrotizing enterocolitis (NEC) is a devastating intestinal disease that occurs primarily in premature infants. We performed genome-resolved metagenomic analysis of 1,163 fecal samples from premature infants to identify microbial features predictive of NEC. Features considered include genes, bacterial strain types, eukaryotes, bacteriophages, plasmids and growth rates. A machine learning classifier found that samples collected prior to NEC diagnosis harbored significantly more Klebsiella, bacteria encoding fimbriae, and bacteria encoding secondary metabolite gene clusters related to quorum sensing and bacteriocin production. Notably, replication rates of all bacteria, especially Enterobacteriaceae, were significantly higher two days before NEC diagnosis. The findings uncover biomarkers that could lead to early detection of NEC and targets for microbiome-based therapeutics.

microbiology↗

bioRxiv2019

Increased Replication Rates of Dissimilatory Nitrogen-Reducing Bacteria Leads to Decreased Anammox Reactor Performance

BackgroundAnaerobic ammonium oxidation (anammox) is a biological process employed to remove reactive nitrogen from wastewater. While a substantial body of literature describes the performance of anammox bioreactors under various operational conditions and perturbations, few studies have resolved the metabolic roles of their core microbial community members. ResultsHere, we used metagenomics to study the microbial community of a laboratory-scale anammox bioreactor from inoculation, through a performance destabilization event, to robust steady-state performance. Metabolic analyses revealed that nutrient acquisition from the environment is selected for in the anammox community. Dissimilatory nitrate reduction to ammonium (DNRA) was the primary nitrogen removal pathway that competed with anammox. Increased replication of bacteria capable of DNRA led to the out-competition of annamox bacteria, and the loss of the bioreactors nitrogen removal capacity. These bacteria were highly associated with the anammox bacterium and considered part of the core microbial community. ConclusionsOur findings highlight the importance of metabolic interdependencies related to nitrogen- and carbon-cycling within anammox bioreactors and the potentially detrimental effects of bacteria that are otherwise considered core microbial community members.

microbiology↗

bioRxiv2019

Functional potential of bacterial strains in the premature infant gut microbiome is associated with gestational age

The gut microbiota of premature and full-term infants have many known differences, but the extent to which the degree of prematurity influences the structure and functional potential of the microbiome has not been deeply explored. Here, we used genome-resolved metagenomics to address how gestational age impacts the premature infant gut microbiome. We found that gestational age is associated with species richness, with more premature infants having lower species richness; this effect lasts until the fourth week of life. Novel Clostridium species and strains related to Streptococcus salivarius and Enterococcus faecalis colonize infants of different gestational ages, and the metabolic potential of these organisms can be distinguished. Thus, we conclude that the extent of prematurity, or directly linked factors, can be an important influence on the microbiome and its functions.

microbiology↗

bioRxiv2018

An archaeal symbiont-host association from the deep terrestrial subsurface

DPANN archaea have reduced metabolic capacities and are diverse and abundant in deep aquifer ecosystems, yet little is known about their interactions with other microorganisms that reside there. Here, we provide evidence for an archaeal host-symbiont association from a deep aquifer system at the Colorado Plateau (Utah, USA). The symbiont, Candidatus Huberiarchaeum crystalense, and its host, Ca. Altiarchaeum hamiconexum, show a highly significant co-occurrence pattern over 65 metagenome samples collected over six years. The physical association of the two organisms was confirmed with genome-informed fluorescence in situ hybridization depicting small cocci of Ca. H. crystalense attached to Ca. A. hamiconexum cells. Based on genomic information, Ca. H. crystalense has a similar metabolism as Nanoarchaeum equitans and potentially scavenges vitamins, sugars, nucleotides, and reduced redox-equivalents from its host. These results provide insight into host-symbiont interactions among members of two uncultivated archaeal phyla that thrive in a deep subsurface aquifer.

microbiology↗

bioRxiv2018

Lipid analysis of CO2-rich subsurface aquifers suggests an autotrophy-based deep biosphere with lysolipids enriched in CPR bacteria

Sediment-hosted CO2-rich aquifers deep below the Colorado Plateau (USA) contain a remarkable diversity of uncultivated microorganisms, including Candidate Phyla Radiation (CPR) bacteria that are putative symbionts unable to synthesize membrane lipids. The origin of organic carbon in these ecosystems is unknown and the source of CPR membrane lipids remains elusive. We collected cells from deep groundwater brought to the surface by eruptions of Crystal Geyser, sequenced the community, and analyzed the whole community lipidome over time. Characteristic stable carbon isotopic compositions of microbial lipids suggest that bacterial and archaeal CO2 fixation ongoing in the deep subsurface provides organic carbon for the complex communities that reside there. Coupled lipidomic-metagenomic analysis indicates that CPR bacteria lack complete lipid biosynthesis pathways but still possess regular lipid membranes. These lipids may therefore originate from other community members, which also adapt to high in situ pressure by increasing fatty acid unsaturation. An unusually high abundance of lysolipids attributed to CPR bacteria may represent an adaptation to membrane curvature stress induced by their small cell sizes. Our findings provide new insights into the carbon cycle in the deep subsurface and suggest the redistribution of lipids into putative symbionts within this community.

microbiology↗

bioRxiv2018

Candidate Phyla Radiation Roizmanbacteria from hot springs have novel, unexpectedly abundant, and potentially alternatively functioning CRISPR-Cas systems

The Candidate Phyla Radiation (CPR) comprises a huge group of bacteria that have small genomes that rarely encode CRISPR-Cas systems for phage defense. Consequently, questions remain about their mechanisms of phage resistance and the nature of phage that infect them. The compact CRISPR-CasY system (Cas12d) with potential value in genome editing was first discovered in these organisms. Relatively few CasY sequences have been reported to date, and little is known about the function and activity of these systems in the natural environment. Here, we conducted a genome-resolved metagenomic investigation of hot spring microbiomes and recovered CRISPR systems mostly from Roizmanbacteria that involve CasY proteins that are divergent from published sequences. Within population diversity in the spacer set indicates current in situ diversification of most of the loci. In addition to CasY, some Roizmanbacteria genomes also encode large type I-B and/or III-A systems that, based on spacer targeting, are used in phage defense. CRISPR targeting identified three phage represented by complete genomes and a prophage, which are the first reported for bacteria of the Microgenomates superphylum. Interestingly, one phage encodes a Cas4-like protein, a scenario that has been suggested to drive acquisition of self-targeting spacers. Consistent with this, the Roizmanbacteria population that it infects has a CRISPR locus that includes self-targeting spacers and a fragmented CasY gene (fCasY). Despite gene fragmentation, the PAM sequence is the same as that of other CasY reported in this study. Fragmentation of CasY may avoid the lethality of self-targeting spacers. However, the spacers may still have some biological role, possibly in genome regulation. The findings expand our understanding of CasY diversity, and more broadly, CRISPR-Cas systems and phage of CPR bacteria.

microbiology↗

bioRxiv2018

Processing of grassland soil C-N compounds into soluble and volatile molecules is depth stratified and mediated by genomically novel bacteria and archaea

Soil microbial activity drives the carbon and nitrogen cycles and is an important determinant of atmospheric trace gas turnover, yet most soils are dominated by organisms with unknown metabolic capacities. Even Acidobacteria, among the most abundant bacteria in soil, remain poorly characterized, and functions across groups such as Verrucomicrobia, Gemmatimonadetes, Chloroflexi, Rokubacteria are understudied. Here, we resolved sixty metagenomic, and twenty proteomic datasets from a grassland soil ecosystem and recovered 793 near-complete microbial genomes from 18 phyla, representing around one third of all organisms detected. Importantly, this enabled extensive genomics-based metabolic predictions for these understudied communities. Acidobacteria from multiple previously unstudied classes have genomes that encode large enzyme complements for complex carbohydrate degradation. Alternatively, most organisms we detected encode carbohydrate esterases that strip readily accessible methyl and acetyl groups from polymers like pectin and xylan, forming methanol and acetate, the availability of which could explain high prevalences of C1 metabolism and acetate utilization in genomes. Organism abundances among samples collected at three soil depths and under natural and amended rainfall regimes indicate statistically higher associations of inorganic nitrogen metabolism and carbon degradation in deep and shallow soils, respectively. This partitioning decreased in samples under extended spring rainfall indicating long term climate alteration can affect both carbon and nitrogen cycling. Overall, by leveraging natural and experimental gradients with genome-resolved metabolic profiles, we link organisms lacking prior genomic characterization to specific roles in complex carbon, C1, nitrate, and ammonia transformations and constrain factors that impact their distributions in soil.

microbiology↗

bioRxiv2018

Microbial communities across a hillslope-riparian transect shaped by proximity to the stream, groundwater table, and weathered bedrock

Watersheds are important suppliers of freshwater for human societies. Within mountainous watersheds, microbial communities impact water chemistry and element fluxes as water from precipitation events discharges through soils and underlying weathered rock, yet there is limited information regarding the structure and function of these communities. Within the East River, CO watershed, we conducted a depth-resolved, hillslope to riparian zone transect study to identify factors that control how microorganisms are distributed and their functions. Metagenomic and geochemical analyses indicate that distance from the East River and proximity to groundwater and underlying weathered shale strongly impact microbial community structure and metabolic potential. Riparian zone microbial communities are compositionally distinct from all hillslope communities. Bacteria from phyla lacking isolated representatives consistently increase in abundance with increasing depth, but only in the riparian zone saturated sediments did we find Candidate Phyla Radiation bacteria. Riparian zone microbial communities are functionally differentiated from hillslope communities based on their capacities for carbon and nitrogen fixation and sulfate reduction. Selenium reduction is prominent at depth in weathered shale and saturated riparian zone sediments. We anticipate that the drivers of community composition and metabolic potential identified throughout the studied transect will predict patterns across the larger watershed hillslope system.

microbiology↗