Metabolic diversity of Ferrovaceae and potential contributions to iron oxidation

Active and abandoned metal and coal mines generate acidic, metal-laden water that pollutes downstream areas, commonly referred to as acid mine drainage (AMD). AMD is host to microbial communities, including acidophilic iron oxidizers. Microbially mediated iron oxidation is a desirable (bio)remediation strategy for AMD. Ferrovaceae are Fe-oxidizing bacteria observed in AMD globally and thus could be an asset for bioremediation strategies. To better understand the potential for Ferrovaceae to contribute to AMD bioremediation, we analyzed 240 genomes and metagenome-assembled genomes from Ferrovaceae, including sequences from AMD sites with high iron oxidation rates. Based on our analyses, the phylogenetic and physiological diversity of this group is greater than previously known. We found that while all taxa are likely capable of iron oxidation using a cyc-2 like protein, some may also be capable of iron oxidation using an Mto-like protein. We also identified Ferrovaceae that are likely capable of anoxygenic phototrophy. Our findings indicate that multiple Ferrovaceae populations co-occur and suggest that differences in physiology may promote niche differentiation along resource axes. Physiologically diverse iron oxidizer communities could support a more resilient microbial community, resulting in higher iron oxidation rates and potentially more efficient bioremediation, and thus our results also indicate that future studies that link taxonomy with iron oxidation activity are warranted.IMPORTANCEAcid mine drainage (AMD) pollutes watersheds worldwide. Microbial communities can be leveraged to improve AMD bioremediation because they drive biogeochemical processes in these ecosystems. In AMD streams, iron-oxidizing microbial populations remove iron from the AMD effluent by precipitating iron oxides, which absorb other metals. These communities vary across sites and differ in how rapidly they oxidize iron. The factors that contribute to iron oxidation rates are not well understood, making it difficult to design effective bioremediation strategies. Ferrovaceae populations are widespread in AMD globally, including in sites with exceptionally high rates of iron oxidation. To examine the potential for Ferrovaceae to be key components of bioremediation strategies, we examined the genomic content and functional potential of Ferrovaceae in publicly available metagenomic data sets. Our analysis uncovered several new species of Ferrovaceae as well as an expanded metabolic potential for this group. Comparative genomics suggests that functional diversity leads to co-occurrence of multiple Ferrovaceae species at the same sites. The presence of multiple iron-oxidizing taxa with distinct physiology could be beneficial for bioremediation strategies.