Isolation and Characterization of a Mo ⁶⁺ -Reducing Bacterium

Abstract

A Mo6+-reducing bacterium (strain 48), which grew on medium supplemented with 200 mM Mo6+, was isolated from stream water obtained from Chengkau, Malaysia. The chemical properties of strain 48 conform to the characteristics of Enterobacter cloacae. Under anaerobic conditions in the glucose-yeast extract medium containing phosphate ion (2.9 mM) and Mo6+ (10 mM), the bacterium reduced Mo6+ to form molybdenum blue. Approximately 27% of Mo6+ added to the medium was reduced after 28 h of cultivation. The reduction of Mo6+ with glucose as an electron donor was strongly inhibited by iodoacetic acid, sodium fluoride, and sodium cyanide, suggesting an involvement of the glycolytic pathway and electron transport in Mo6+ reduction. NADH and N,N,N',N'-tetramethyl-p-phenylenediamine served as electron donors for Mo6+ reduction. When NADH was used as an electron donor, at first cytochrome b in the cell extract was reduced, and then molybdenum blue was formed. Sodium cyanide strongly inhibited Mo6+ reduction by NADH (5 mM) but not the reduction of cytochrome b in the cell extract, suggesting that the reduced component of the electron transport system after cytochrome b serves as an electron donor for Mo6+ reduction. Both ferric and stannous ions strongly enhanced the activity of Mo6+ reduction by NADH.

Molybdate reduction byPseudomonassp. strain DRY2

“…We repeated the experiment using molybdate as the electron-accepting substrate (Ghani et al 1993) instead of laboratory-prepared phosphomolybdate in the enzyme assay, and obtained similar results with no inhibition of molybdate-reducing activity seen (data not shown).…”

“…cloacae strain 48 and Ser. marcescens strain DRY6 with the optimal ratio of molybdate to phosphate ions found to be between 15 and 25 and between 2AE9 and 5 mmol l )1 , respectively (Ghani et al 1993;Shukor et al 2008b). Campbell et al (1985) reported that at 5 mmol l )1 phosphate, 80 mmol l )1 molybdate was the optimum concentration for supporting molybdate reduction in E. coli K12.…”

“…In contrast, it was reported that sucrose is the best electron donor for Ent. cloacae strain 48 (Ghani et al 1993) and Ser. marcescens strain DRY6 (Shukor et al 2008b).…”

“…According to Levine (1925), molybdate reduction was first reported in Eschericia coli by Capaldi and Proskauer (1896). This is followed by other bacteria (Woolfolk and Whiteley 1962;Bautista and Alexander 1972;Campbell et al 1985;Sugio et al 1988;Ghani et al 1993;Lloyd 2003). Recently, we have isolated and characterized another molybdenum-reducing bacterium from Malaysian soils (Shukor et al 2008b).…”

“…To solve this problem, we adapted the method of Munch and Ottow (1983) and discovered that the reduction of molybdate in Enterobacter cloacae strain 48 is enzymatic (Shukor et al 2002). Bacterial reduction of molybdenum to Mo-blue has been suggested as an important remediation tool for cleaning up molybdenum pollutant in the environment (Ghani et al 1993;Neunhäuserer et al 2001). However, screening of more potent reducers is required to develop a cost-effective bioremediation strategy.…”