Hexavalent chromate bioreduction by a magnetotactic bacterium Magnetospirillum gryphiswaldense MSR-1 and the effect of magnetosome synthesis.

Magnetotactic bacteria (MTB) are receiving attention for heavy metal biotreatment due to their potential for biosorption with heavy metals and the capability of the magnetic recovery. In this study, we investigated the characteristics of Cr(VI) bioreduction and biosorption by an MTB isolate, Magnetospirillum gryphiswaldense MSR-1, which has a higher growth rate and wider reflexivity in culture conditions. Our results demonstrated that the MSR-1 strain could remove Cr(VI) up to the concentration of 40 mg L and with an optimal activity at neutral pH conditions. The magnetosome synthesis existed regulatory mechanisms between Cr(VI) reduction and cell division. The addition of 10 mg L Cr(VI) significantly inhibited cell growth, but the magnetosome-deficient strain, B17316, showed an average specific growth rate of 0.062 h at the same dosage. Cr(VI) reduction examined by the heat-inactivated and resting cells demonstrated that the main mechanism for MSR-1 strain to reduce Cr(VI) was chromate reductase and adsorption, and magnetosome synthesis would enhance the chromate reductase activity. Finally, our results elucidated that the chromate reductase distributes diversely in multiple subcellular components of the MSR-1 cells, including extracellular, membrane-associated, and intracellular cytoplasmic activity; and expression of the membrane-associated chromate reductase was increased after the cells were pre-exposed by Cr(VI).