Chromate Interaction with the Chromate Reducing Actinobacterium Intrasporangium chromatireducens Q5-1

This study was conducted to determine the microbe-chromate [Cr(VI)] interaction and the effect of quinoid analogue anthraquinone-2-sulfonate (AQS) on aerobic Cr(VI) reduction by Intrasporangium chromatireducens Q5-1. The addition of redox mediator AQS, which might expedite the electron transfer, promoted Cr(VI) bioreduction. Addition of carbon sources, such as maltose, acetate, sucrose and lactose stimulated the AQS-promoted Cr(VI) reduction of strain Q5-1. Induction experiment clarified that the enzyme involves in the Cr(VI) reduction is constitutive. Energy-dispersive spectroscopy (EDS) spectra showed the existence of trace Cr distributed on the cell surface. X-ray photoelectron spectroscopy (XPS) analysis revealed that the Cr(III) complex was bound to the cell surface (0.87%, atomic percent). The spectra shifts detected by Fourier transform infrared (FTIR) spectroscopy indicated that Cr(III) was bound to the carbonyl and amide groups. In addition, Cr(VI) reduction by different cell fractions showed that Cr(VI) reduction was occurred extracellularly rather than intracellularly. The results disclosed that Cr(VI) detoxification of strain Q5-1 was mainly associated with extracellular Cr(VI) reduction process in combination with trace Cr(III) adsorption on the cell surface. A schematic figure depicting the interactions between strain Q5-1 and Cr(VI) was presented. This study enhanced the understanding of the microbe-Cr(VI) interaction mechanism and revealed the AQS-promoted aerobic Cr(VI) reduction of strain Q5-1. Such strain and quinoid analogue-mediated bacterial Cr(VI) reduction may facilitate the bioremediation for Cr(VI)-polluted environment.