Fe (III) and Se (IV) reduction by Desulfitobacterium hafniense (DCB-2)

Desulfitobacterium hafniense (DCB-2) is a motile Gram-positive, anaerobic, sulfur-reducing bacterium that can survive adverse conditions through its ability to sporulate. Originally studied for its ability to dehalogenate, the full bioremediation potential of D. hafniense has yet to be explored. Of particular interest to bioremediation is the ability of D. hafniense to reduce metals. Two metals, iron and selenium, were selected to gain insight into the metal reducing abilities of D. hafniense. D. hafniense reduces iron during respiration as its sole terminal electron acceptor. Reduction of Se(VI) can occur by D. hafniense when grown fermentatively with Se(VI) as an electron sink. Cellular morphology changes when presented with 50 mM Fe(III) or 1 mM Se(VI) as compared to growth fermentatively with pyruvate were observed for D. hafniense using scanning electron microscopy and transmission electron microscopy. The localization of the metals as related to cellular morphology was further analyzed using X-ray energy dispersive spectrometry coupled to electron microscopy, which found the metals to be associated with extracellular structures, such as membrane-bound vesicles for Se(VI) reduction. Using microarrays developed for the D. hafniense genome, studies were performed on D. hafniense cultures grown in the presence of 50 mM Fe(III) or 1 mM Se(VI) to elucidate key genes involved in these metal reductions. Examples of highly up-regulated genes during Se(VI) reduction by D. hafniense include a radical SAM-type protein and a heavy metal response regulator consisting of a CheY-like receiver domain and a HTH DNA-binding domain. More findings and implications are detailed in the poster.