Heavy Metal Removal by Magnetospirillum Strains and its Possible Use in the Treatment of Tannery Effluents

Abstract

Heavy metals pose a serious threat to the environment and their continuous accumulation cause ecological imbalance. Biosorption of heavy metals by bacteria is a conventional process. However, the meagre performance of bacterial biomass in situ limits their applications. Magnetotactic bacteria are microaerophilic organism that possesses an active metal transport system for the biomineralization of iron oxide particles. On this basis, this work investigates the ability of chosen Magnetospirillum strains, viz, MSR-1 RJS2, RJS5, RJS6, and RJS7 to uptake the heavy metals through biomineralization. Metals such as cadmium, lead, zinc, manganese, nickel, chromium, and cobalt were supplemented independently (1 ppm and 10 ppm) in previously optimized MS1 media as a sole electron donor and its utilization by the bacteria were determined by Atomic Absorption Spectroscopy (AAS). Further, the optimal time/days and metal concentration for efficient biosorption were optimized. All the strains were grown in presence of metals and the growth pattern was found to be unaltered due to metal concentration. The AAS analysis revealed metal biosorption (1 ppm) by all five strains. RJS5 strain utilized all the metals viz, cadmium (95.8%), manganese (39.3%), lead (58%), nickel (57%), zinc (55%), chromium (27.5%) and cobalt (78%). Similarly, RJS2 strain showed metal biosorption in cadmium (26.4%), manganese (28%), lead (96%), nickel (30%), zinc (9.2%), chromium (51%) and cobalt (48%). The strain MSR-1 displayed biosorption of five metals- chromium (100%), cadmium (55%), manganese (12%), cobalt (40%) and nickel (4%). Both RJS6 and RJS7 displayed significant biosorption of six metals˗ cadmium (52%), manganese (17.2%), nickel (10%), zinc (34%), chromium (100%) and cobalt (59%) and cadmium (24%), manganese (22%), nickel (7.8%), zinc (40%), chromium (69%) and cobalt (28%) respectively. Metal biosorption in MSR-1 was higher in 10 ppm than 1 ppm concentration. Moreover, metals – lead and nickel biosorption was more evident in 10 ppm concentration by MTBs. RJS5 being the effective strain was exposed to a high concentration of lead, cadmium, and zinc. AAS analysis revealed the biosorption of lead (93.42%) at a 50 ppm concentration. The strains were further exposed for metal biosorption from tannery effluents. RJS6 showed higher biosorption of metals compared to other strains with nickel (88%) and zinc (81%). RJS2 displayed significant biosorption of manganese (82%) and cobalt (96%). The other three strains MSR-1, RJS5, and RJS7 showed moderate biosorption of metals from tannery effluent. The MTB strains showed biosorption against all the metals from tannery effluent. The ability of these strains to remove heavy metals from industrial waste can be further explored for a clean environment.