Biology subjects

Crits-Christoph, A.

Publications and source records attributed to Crits-Christoph, A..

26 records · Page 2Linked to original sources

bioRxiv2020

Meanders as a scaling motif for understanding of floodplain soil microbiome and biogeochemical potential at the watershed scale

Biogeochemical exports of C, N, S and H2 from watersheds are modulated by the activity of microorganisms that function over micron scales. This disparity of scales presents a substantial challenge for development of predictive models describing watershed function. Here, we tested the hypothesis that meander-bound regions exhibit patterns of microbial metabolic potential that are broadly predictive of biogeochemical processes in floodplain soils along a river corridor. We intensively sampled floodplain soils located in the upper, middle, and lower reaches of the East River in Colorado and reconstructed 248 draft quality genomes representative at a sub-species level. Approximately one third of the representative genomes were detected across all three locations with similar levels of abundance, and despite the very high microbial diversity and complexity of the soils, ~15% of species were detected in two consecutive years. A core floodplain microbiome was enriched in bacterial capacities for aerobic respiration, aerobic CO oxidation, and thiosulfate oxidation with the formation of elemental sulfur. We did not detect systematic patterns of gene abundance based on sampling position relative to the river. However, at the watershed scale meander-bound floodplains appear to serve as scaling motifs that predict aggregate capacities for biogeochemical transformations in floodplain soils. Given this, we conducted a transcriptomic analysis of the middle site. Overall, the most highly transcribed genes were amoCAB and nxrAB (for nitrification) followed by genes involved in methanol and formate oxidation, and nitrogen and CO2 fixation. Low soil organic carbon correlated with high activity of genes involved in methanol, formate, sulfide, hydrogen, and ammonia oxidation, nitrite oxidoreduction, and nitrate and nitrite reduction. Thus, widely represented genetic capacities did not predict in situ activity at one time point, but rather they define a reservoir of biogeochemical potential available as conditions change.

microbiology↗

bioRxiv2020

Large Freshwater Phages with the Potential to Augment Aerobic Methane Oxidation

There is growing evidence that phages with unusually large genomes are common across various natural and human microbiomes, but little is known about their genetic inventories or potential ecosystem impacts. Here, we reconstructed large phage genomes from freshwater lakes known to contain bacteria that oxidize methane. Twenty-two manually curated genomes (18 are complete) ranging from 159 to 527 kbp in length were found to encode the pmoC gene, an enzymatically critical subunit of the particulate methane monooxygenase, the predominant methane oxidation catalyst in nature. The phage-associated PmoC show high similarity (> 90%) and affiliate phylogenetically with those of coexisting bacterial methanotrophs, and their abundance patterns correlate with the abundances of these bacteria, supporting host-phage relationships. We suggest that phage PmoC has similar functions to additional copies of PmoC encoded in bacterial genomes, thus contribute to growth on methane. Transcriptomics data from one system showed that the phage-associated pmoC genes are actively expressed in situ. Augmentation of bacterial methane oxidation by pmoC-phages during infection could modulate the efflux of this powerful greenhouse gas into the environment.

microbiology↗

bioRxiv2020

InStrain enables population genomic analysis from metagenomic data and rigorous detection of identical microbial strains

Coexisting microbial cells of the same species often exhibit genetic differences that can affect phenotypes ranging from nutrient preference to pathogenicity. Here we present inStrain, a program that utilizes metagenomic paired reads to profile intra-population genetic diversity (microdiversity) across whole genomes and compare populations in a microdiversity-aware manner, dramatically increasing genomic comparison accuracy when benchmarked against existing methods. We use inStrain to profile >1,000 fecal metagenomes from newborn premature infants and find that siblings share significantly more strains than unrelated infants, although identical twins share no more strains than fraternal siblings. Infants born via cesarean section harbored Klebsiella with significantly higher nucleotide diversity than infants delivered vaginally, potentially reflecting acquisition from hospital versus maternal microbiomes. Genomic loci showing diversity within an infant included variants found in other infants, possibly reflecting inoculation from diverse hospital-associated sources. InStrain can be applied to any metagenomic dataset for microdiversity analysis and rigorous strain comparison.

microbiology↗

bioRxiv2019

Bacterial secondary metabolite biosynthetic potential in soil varies with phylum, depth, and vegetation type

Bacteria isolated from soils are major sources of specialized metabolites, including antibiotics and other compounds with clinical value that likely shape interactions among microbial community members and impact biogeochemical cycles. Yet, isolated lineages represent a small fraction of all soil bacterial diversity. It remains unclear how the production of specialized metabolites varies across the phylogenetic diversity of bacterial species in soils, and whether the genetic potential for production of these metabolites differs with soil type. We sampled soils and saprolite from three sites in a northern California Critical Zone Observatory with varying vegetation and bedrock characteristics and used metagenomic sequencing and assembly to reconstruct 1,334 microbial genomes containing diverse biosynthetic gene clusters (BGCs) for secondary metabolite production. We obtained genomes for prolific producers of secondary metabolites, including novel groups within the Actinobacteria, Chloroflexi and candidate phylum Dormibactereota. Surprisingly, one genome of a Candidate Phyla Radiation bacterium encoded for a ribosomally synthesized linear azole/azoline-containing peptide, a capacity we found in other publicly available CPR bacterial genomes. Overall, bacteria with higher biosynthetic potential were enriched in shallow soils and grassland soils, with patterns of abundance of BGC type varying by taxonomy.

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

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

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↗

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↗