The chemolithoautotrophic bacterium CB1MN can utilize hydrogen and sulfur as electron donors with ferric iron as electron acceptor

Abstract

Microbially mediated redox processes of sulfur compounds are closely related to the occurrence of iron oxides in natural ecosystems. However, so far, no pure culture has been reported to couple sulfur oxidation to iron reduction under neutral or alkaline conditions. Here, we report on a pure culture of a sulfur-oxidizing and iron-reducing bacterium (strain CB1MN) and demonstrate that hydrogen can be used as an electron donor supporting the growth of strain CB1MN with ferrihydrite as electron acceptor. The reduction of ferrihydrite by CB1MN produced dissolved Fe(II) and secondary minerals, which was confirmed by Raman analysis. In addition, strain CB1MN can also utilize a few organic carbon and electron sources such as glucose, pyruvate, acetate, and succinate for maintaining growth and metabolic activity with sulfite as electron acceptor. Genomic analysis showed that a membrane-bound Hyd-4-type hydrogenase and a cytoplasmic F420-non-reducing hydrogenase should be responsible for the hydrogen oxidation. Furthermore, a large number of genes encoding type IV pili and flagella were suspected to be involved in electron transport. Our results imply that the sulfur- and iron-utilizing chemoautotrophs not only use sulfur compounds for energy conservation, but hydrogen and organic carbon sources can be electron donors.