Hexavalent chromium reduction by an actinobacterium Flexivirga alba ST13T in the family Dermacoccaceae

An isolated strain Flexivirga alba ST13T was examined for the reducing activity of hexavalent chromium (Cr(VI)). Strain ST13T grew in the liquid medium containing 0.33 mM Cr(VI) under aerobic cultivation, even though growth was inhibited on agar minimal media containing 0.31 mM Cr(VI). The growth in the liquid medium containing Cr(VI) at 3 mM was severely inhibited, and the concentration of Cr(VI) decreased below the detection limit within 13 days. Most of the Cr(VI) was eliminated from the liquid medium in the log phase and the stationary phase. XANES analysis of the precipitate shows the presence of Cr(OH)3, indicating the bacterial reduction of Cr(VI) to trivalent chromium (Cr(III)). The bacterial Cr(VI) reduction was more efficient in minimal medium supplemented with molasses than with glucose. These results strongly suggest that the isolate F. alba ST13T is a novel actinobacterium with Cr(VI) reducing activity that is stimulated by molasses.