Genomic evidence for a chemical link between redox conditions and microbial community composition

Environmental influences on community structure are often assessed through multivariate analyses in order to relate microbial abundances to separately measured physicochemical variables. However, genes and proteins are themselves chemical entities; in combination with genome databases, differences in microbial abundances directly encode for chemical variability. We predicted that the carbon oxidation state of inferred community proteomes, obtained by combining taxonomic abundances from published 16S rRNA gene sequencing datasets with predicted microbial proteomes from the NCBI Reference Sequence (RefSeq) database, would reflect environmental oxidation-reduction conditions in various natural and engineered settings including shale gas wells. Our analysis confirms the geobiochemical predictions for environmental redox gradients within and between hydrothermal systems and stratified lakes and marine environments. Where they are present, a common set of taxonomic groups (Gamma- and Deltaproteobacteria and Clostridia) act as drivers of the community-level differences in oxidation state, whereas Flavobacteria most often oppose the overall changes. The geobiochemical signal is largest for the steep redox gradients associated with hydrothermal systems and between surface water and produced fluids from shale gas wells, demonstrating the ability to determine the magnitude of redox effects on microbial communities from 16S sequencing alone.