Reduction of Cr(VI) by immobilized cells of Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776

Abstract

Hexavalent chromium, a carcinogen and mutagen, can be reduced to Cr(III) by Desulfovibrio vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776. This study examined Cr(VI) reduction by immobilized cells of the two strains in a common solution matrix using various entrapment matrices. Chitosan and PVA-borate beads did not retain integrity and supported low or no reduction of Cr(VI) by the cells. A commercial preparation (Lentikats) was stable but also did not support Cr(VI) reduction. K-carrageenan beads were stable in batch suspensions but gel integrity was lost after only 5 h in a flow-through system in the presence of 100 microM Cr(VI). The best immobilization matrices were agar and agarose, where the initial rates of reduction of Cr(VI) (from 500 microM solution) for D. vulgaris NCIMB 8303 and Microbacterium sp. NCIMB 13776 were 127 (agar) and 130 (agarose), and 15 (agar) and 12 (agarose) nmol h(-1) mg dry cell wt(-1), respectively. The higher removal of Cr(VI) by D. vulgaris was also seen in 14-mL packed-bed flow-through columns, where, at a flow rate of 2.4 mL h(-1), the percentage removal of Cr(VI) was approximately 95% and 60% for D. vulgaris and Microbacterium sp., respectively (agar-immobilized cells). The Cr(VI) reducing activities of D. vulgaris and Microbacterium sp. were lost after 159 and 140 h, respectively. Examination of the beads for structural integrity within the columns in situ using magnetic resonance imaging after 24 and 100 h of continuous operation against Cr(VI) (with negligible Cr retained within the columns) showed that agar beads were more stable with time. The most appropriate system for development of a continuous bioprocess is thus the use of D. vulgaris NCIMB 8303 immobilized in an agar gel matrix.

Potential Production of Ethanol by Saccharomyces cerevisiae Immobilized and Coimmobilized with Zymomonas mobilis: Alternative for the Reuse of a Waste Organic

“…The immobilization cell technologies have been applied for diferent purposes as for the production of hydrogen [12] and compounds commercially used in the food industry [13]. Other studies have been developed with immobilized algal cells to remove nutrients (N and P) from wastewater, phenol and hexavalent chromium [14][15][16][17]. Similarly, the immobilization of Zymomonas and Saccharomyces have been used for the bio-ethanol production from waste materials [7][8][9][10][18][19][20].…”

Hexavalent chromium reduction by immobilized cells of Bacillus sphaericus AND 303

“…Cells immobilized in PVA, PVB, CA, agarose and agar-agar beads were tested for Cr(VI) reduction in batch experiments following the procedure of Humphries et al (2005). The beads were washed three times with sterile distilled water and added aseptically to 100 ml of Erlenmeyer flask containing 10 ml of mineral salts broth supplemented with 20 µM Cr(VI) and 0.1 % glucose as electron donor.…”

“…This general trend of enhanced chromate reduction with increase in cell density in the matrices was evident with the cells of B. coagulans (Philip et al 1999) and Microbacterium sp. (Humphries et al 2005) immobilized in polyacrylamide and PVA alginate respectively. …”

“…2) could be attributed to the loss of matrix stability as well as release of B. sphaericus cells and reductase in the long term shaking incubation and repeated wash as observed in Pseudomonas aeruginosa (Pang et al 2011), Desulfovibrio vulgaris and Microbacterium sp. (Humphries et al 2005) The deterioration or changes of biochemical features of the strain during the process of reduction could be another possibility (Pang et al 2011). The understanding of this phenomenon could be used to improve the stability of B. sphaericus cells in order to apply it in an efficient continuous reduction system.…”

“…have been used for Cr reduction and proved to be effective. These immobilized cells being more stable, can be reused and are easy to regenerate with easier solid-liquid separation (Humphries et al 2005;Elangovan et al 2010). Under immobilized conditions, cells are protected against the excessive toxic action of high chromate concentration and thereby improve the cellular activities compared with free cells.…”