D J . M. MY E RS . 2000. Shewanella putrefaciens MR-1 can reduce a diverse array of compounds under anaerobic conditions, including manganese and iron oxides, fumarate, nitrate, and many other compounds. These reductive processes are apparently linked to a complex electron transport system. Chromium (Cr) is a toxic and mutagenic metal and bacteria could potentially be utilized to immobilize Cr by reducing the soluble and bioavailable state, Cr(VI), to the insoluble and less bioavailable state, Cr(III). Formate-dependent Cr(VI) reductase activity was detected in anaerobically grown cells of S. putrefaciens MR-1, with highest 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 mmol l −1 FMN markedly stimulated formate-dependent Cr(VI) reductase, and the activity was almost completely inhibited by diphenyliodonium chloride, an inhibitor of flavoproteins. Cr(VI) reductase activity was also inhibited by pchloromercuriphenylsulphonate, 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 paramagnetic resonance (EPR) spectroscopy, suggesting a one-electron reduction as the first step.
C h a rles R . M y ers, B j Èor n Por g ils son , B ria n P. C a rs t en s, a n d J u d it h M . M yers D e p a r t m e n t of P h a r m a c olog y a n d Tox icology, M e d ic a l C ollege of W isc on s in , M ilw a u k e e, W isc on s in , U S A 10 7 6 -9 1 88 /99 $1 2.0 0 + .0 0 1 0 3
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