Cr. Myers et al., Chromium(VI) reductase activity is associated with the cytoplasmic membrane of anaerobically grown Shewanella putrefaciens MR-1, J APPL MICR, 88(1), 2000, pp. 98-106
Shewanella putrefaciens MR-1 can reduce a diverse array of compounds under
anaerobic conditions, including manganese and iron oxides, fumarate, nitrat
e, and many other compounds. These reductive processes are apparently linke
d to a complex electron transport system. Chromium (Cr) is a toxic and muta
genic metal and bacteria could potentially be utilized to immobilize Cr by
reducing the soluble and bioavailable state, Cr(VI), to the insoluble and l
ess bioavailable state, Cr(III). Formate-dependent Cr(VI) reductase activit
y was detected in anaerobically grown cells of S. putrefaciens MR-1, with h
ighest specific activity in the cytoplasmic membrane. Both formate and NADH
served as electron donors for Cr(VI) reductase, whereas l-lactate or NADPH
did not support any activity. The addition of 10 mu mol l(-1) FMN markedly
stimulated formate-dependent Cr(VI) reductase, and the activity was almost
completely inhibited by diphenyliodonium chloride, an inhibitor of flavopr
oteins. Cr(VI) reductase activity was also inhibited by p-chloromercuriphen
ylsulphonate, azide, 2-heptyl-4-hydroxyquinolone-N-oxide, and antimycin A,
suggesting involvement of a multi-component electron transport chain which
could include cytochromes and quinones. Cr(V) was detected by electron para
magnetic resonance (EPR) spectroscopy, suggesting a one-electron reduction
as the first step.