Composition and Activity of an Autotrophic Fe(II)-Oxidizing, Nitrate-Reducing Enrichment Culture

16S rRNA gene libraries from the lithoautotrophic Fe(II)-oxidizing, nitrate-reducing enrichment culture described by Straub et al. (K.L. Straub, M. Benz, B. Schink, and F. Widdel, Appl. Environ. Microbiol. 62: 1458-1460, 1996) were dominated by a phylotype related (95% 16S rRNA gene homology) to the autotrophic Fe(II) oxidizer Sideroxydans lithotrophicus. The libraries also contained phylotypes related to known heterotrophic nitrate reducers Comamonas badia, Parvibaculum lavamentivorans, and Rhodanobacter thiooxidans. The three heterotrophs were isolated and found to be capable of only partial (12 to 24%) Fe(II) oxidation, suggesting that the Sideroxydans species has primary responsibility for Fe(II) oxidation in the enrichment culture.