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Title: Hydrogenase activity of mineral-associated and suspended populations of Desulfovibrio Desulfuricans Essex 6

item Reardon, Catherine - Kate
item MAGNUSON, TIMOTHY - Idaho State University
item BOYD, ERIC - Montana State University
item LEAVITT, WILLIAM - Harvard University
item REED, DAVID - Idaho National Laboratory
item GEESEY, GILL - Montana State University

Submitted to: Microbial Ecology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/1/2013
Publication Date: 11/6/2013
Citation: Reardon, C.L., Magnuson, T.S., Boyd, E.S., Leavitt, W.D., Reed, D.W., Geesey, G.G. 2013. Hydrogenase activity of mineral-associated and suspended populations of Desulfovibrio Desulfuricans Essex 6. Microbial Ecology. 67(2):318-326.

Interpretive Summary: Sulfate reducing bacteria (SRB) are a diverse group of microbes that have significant industrial and environmental impacts. SRB produce sulfide from the metabolism of sulfate. Sulfide, which is highly corrosive, not only contributes to the biocorrosion of metals but affects the type and solubility of minerals and metals in the environment. Sulfide reacts rapidly with iron to form ferrous sulfide minerals. Several factors control the type and stability of the ferrous sulfides that are formed. These factors include the concentrations of sulfide and soluble iron, the pH, and redox potential, all which can be affected by microbial activity. SRB commonly grow on particle surfaces. The ferrous sulfides that are formed by cells attached to a mineral surface are different than those formed by cells growing in a suspension. In order to identify why the ferrous sulfides are different, we analyzed the activity of a cellular enzyme that can potentially influence the conditions near the cell. The enzyme hydrogenase catalyzes reversible reaction H2 ' 2H+ + 2e- and can transfer energy or electrons directly to metals. The hydrogenase activity of the SRB Desulfovibrio desulfuricans strain Essex 6 was compared when cells were cultured under sulfate-reducing (sulfide-producing) or pyruvate fermenting (non-sulfide-producing) conditions in the presence or absence of hematite, an iron oxide mineral. The hydrogenase activity of cells attached to the hematite surface was

Technical Abstract: The interactions between sulfate-reducing microorganisms and iron oxides influence a number of important redox-sensitive biogeochemical processes including the formation of iron sulfides. Enzymes, such as hydrogenase which catalyze the reversible oxidation of molecular hydrogen, are known to mediate electron transfer to metals and may contribute to the formation and speciation of ferrous sulfide formed at the cell-mineral interface. The present study describes the effect of growth on a hematite surface on whole cell hydrogenase activity associated with different metabolic pathways in Desulfovibrio desulfuricans strain Essex 6. Hematite-associated cells exhibited significantly greater hydrogenase activity than suspended populations during sulfate respiration but not pyruvate fermentation. The enhanced activity of the hematite-associated, sulfate-grown cells appears to be dependent on iron availability rather than a general response to surface attachment since the activity of glass-associated cells did not differ from that of suspended populations. Hydrogenase activity of pyruvate-fermenting cells was stimulated by addition of iron as soluble Fe(II)Cl2 and, in the absence of added iron, both sulfate-reducing and pyruvate-fermenting cells displayed similar rates of hydrogenase activity. These data suggest that iron exerts a stronger influence on whole cell hydrogenase activity than either metabolic pathway or surface-associated growth. The localization of hydrogenase to the cell envelope and the enhanced activity at the mineral surface in sulfate-reducing cells may contribute to the speciation of iron sulfides formed under these different growth phases.