title: Reduction of hexavalent chromium by cell-free extract of Bacillus sphaericus AND 303 isolated from serpentine soil.
abstract: Cell-free extracts (CFEs) of chromium-resistant bacterium Bacillus sphaericus AND 303 isolated from serpentine soil of Andaman, India reduced Cr(VI) in in vitro condition, and the reductase activity was solely localized in the soluble cell-fractions (S12, S32, and S150). The enzyme was constitutive as the CFEs from cells grown in Cr(VI)-free and Cr(VI)-containing media reduced a more or less equal amount of Cr(VI). Optimum Cr(VI) reductase activity was obtained at an enzyme (S150) concentration equivalent to 4.56 mg protein/mL, 300 microM: Cr(VI) and pH 6.0 after 30 min incubation at 30 degrees C. The enzyme was heat labile; 80% of its activity was lost when exposed at 70 degrees C for 15 min. Kinetics of Cr(VI) reductase activity fit well with the linearized Lineweaver-Burk plot and showed a V(max) of 1.432 micromol Cr(VI)/mg protein/min and K(m) of 158.12 microM: Cr(VI). The presence of additional electron donors accelerated Cr(VI) reductase activity of CFE, and an increase of 28% activity over control was recorded with 1.0 microM: NADH. Heavy metal ions such as Ni(II), Cu(II), and Cd(II) were strong inhibitors of Cr(VI) reductase unlike that of 100 microM: Co(II), which retained 93% activity over control.
authors.affiliation: Microbiology Laboratory, Department of Botany, University of Calcutta, 35 Ballygunge Circular Road, Kolkata 700 019, India.
authors.forename: Arundhati
authors.initials: A
authors.lastname: Pal
authors.forename: Sumana
authors.initials: S
authors.lastname: Dutta
authors.forename: A K
authors.initials: AK
authors.lastname: Paul
mesh_terms: D000900:Anti-Bacterial Agents / Q000378:metabolism / Q000494:pharmacology; D001407:Bacillus / Q000201:enzymology* / Q000302:isolation & purification / Q000378:metabolism*; D002457:Cell Extracts / Q000302:isolation & purification*; D002857:Chromium / Q000378:metabolism* / Q000494:pharmacology; D024881:Drug Resistance, Bacterial; D020536:Enzyme Activators; D004791:Enzyme Inhibitors / Q000494:pharmacology; D004795:Enzyme Stability; D006358:Hot Temperature; D006863:Hydrogen-Ion Concentration; D007194:India; D007700:Kinetics; D008670:Metals / Q000494:pharmacology; D009243:NAD / Q000494:pharmacology; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000032:analysis*; D012988:Soil Microbiology; D013696:Temperature; D013997:Time Factors
chemical_list: D000900:Anti-Bacterial Agents; D002457:Cell Extracts; D020536:Enzyme Activators; D004791:Enzyme Inhibitors; D008670:Metals; D002857:Chromium; D009243:NAD; C074702:chromium hexavalent ion; D010088:Oxidoreductases