NETWORKED MICROBIAL INTERACTIONS AND BIOGEOCHEMICAL CYCLING IN MODERN AND ANCIENT FERRUGINOUS ENVIRONMENTS

Precambrian microbial communities and the impact they had on global geochemical cycles over 3 billion years of Earth’s history remain largely conceptual due to a lack of studies in analogue environments. Kabuno Bay, a sub-basin of Lake Kivu, which borders Rwanda and the Democratic Republic of Congo, is one of the few permanently stratified iron-rich (ferruginous) environments on the planet today. Process rate measurements and tag sequencing reveal a tight coupling between the primary producing photoferrotrophic bacteria and heterotrophic iron reducers or methanogens. One of these primary producing photoferrotrophs, Chlorobium phaeoferrooxidans stain KB01 has been brought into pure culture enabling laboratory studies of its physiological potential. Other than strain KB01, however, the organisms that couple C and Fe cycling in Kabuno Bay remain largely unknown. Our new metagenomic analyses from the Kabuno Bay water column shed light on the genetic potential of key members of this microbial community. Pathway-centric analyses highlight the diverse taxa that drive carbon fixation, organic carbon degradation, Fe recycling and C1 carbon metabolisms. Collectively, our metagenomic analyses in Kabuno Bay imply metabolic coupling that likely supported microbial communities across vast stretches of Earth’s early history.