Genomic and transcriptomic evidence for niche partitioning among sulfate-reducing bacteria in redox-stratified cyanobacterial mats of the Middle Island Sinkhole

Abstract

Sulfate-reducing bacteria (SRB) often shape the biogeochemistry of cyanobacterial mats through metabolic interactions and production of sulfide. Nevertheless, the ecology and physiology of sulfate-reducers inhabiting microbial mats remains poorly understood. For instance, in cyanobacterial mats inhabiting the Middle Island Sinkhole (MIS) in Lake Huron, some of the largest knowledge gaps regarding SRB involve the controls of their distribution, diversity, and metabolic activities with respect to a changing geochemical profile of oxygen and sulfide during diel cycles. Metagenomic and metatranscriptomic approaches offer high potential to close such knowledge gaps and to understand the genomic potential and activity of SRB better. Through genomic binning of metagenomic data from MIS cyanobacterial mats, I identified 8 draft genomes of SRB. Transcriptomic reads were recovered from day and night microbial mat samples and mapped to the SRB genomes, revealing gene transcripts associated with use of electron donors such as H2 and various organic carbon compounds and use of electron acceptors such as nitrate and sulfate. The data presented here show patterns of niche partitioning in SRB, which is likely an important factor in controlling SRB diversity in cyanobacterial mats. This research enhances our understanding of microbial ecology and biogeochemistry in cyanobacterial mats and has implications for geobiology of both the modern and ancient Earth.