Characterization of a neutrophilic, chemolithoautotrophic Fe(II)-oxidizing beta-proteobacterium from freshwater wetland sediments

A neutrophilic Fe( II)- oxidizing bacterium ( FeOB) isolated from Fe- rich freshwater wetland sediments has been phylogenetically and physiologically characterized. The 16S rRNA gene sequence of this organism ( designated strain TW2) places it among the Rhodocyclus group within the beta- proteobacteria. The closest known relative to strain TW2 is the heterotrophic perchlorate reducer Dechlorosoma suillum, with 94% 16S rRNA gene identity. TW2 grows chemolithoautotrophically with Fe( II) as an electron donor and O-2 as an electron acceptor. Inorganic carbon fixation during growth on Fe( II) was demonstrated via (HCO-)-C-14 (3) fixation experiments. The organism can also grow organotrophically with acetate as the sole carbon and energy source, and can utilize acetate as an auxiliary source of fixed carbon which enhances cell yield ( 2 - 3- fold) during lithotrophic growth on Fe( II). No other electron donors and no electron acceptors other than O-2 were utilized. The organism's ability to grow with Fe( II) and acetate, along with its limitations with respect to electron acceptor utilization, suggests a specific adaptation to microaerobic niches in redox interfacial environments. The unique metabolism of strain TW2, together with the 16S rRNA sequence data, suggests that this organism represents a novel taxonomic group at the genus level.