Novel insights into the taxonomic diversity and molecular mechanisms of bacterial Mn(III) reduction

Soluble ligand-bound Mn(III) can support anaerobic microbial respiration in diverse aquatic environments. Thus far, Mn(III) reduction has only been associated with certainGammaproteobacteria. Here, we characterized microbial communities enriched from Mn-replete sediments of Lake Matano, Indonesia. Our results provide the first evidence for the biological reduction of soluble Mn(III) outside theGammaproteobacteria. Metagenome assembly and binning revealed a novel betaproteobacterium, which we designate 'CandidatusDechloromonas occultata.' This organism dominated the enrichment and expressed a porin-cytochromeccomplex typically associated with iron-oxidizingBetaproteobacteriaand a novel cytochrome c-rich protein cluster (Occ), including an undecaheme putatively involved in extracellular electron transfer. Thisoccgene cluster was also detected in diverse aquatic bacteria, including uncultivatedBetaproteobacteriafrom the deep subsurface. These observations provide new insight into the taxonomic and functional diversity of microbially driven Mn(III) reduction in natural environments.