Abstract: Objective:To investigate the growth of Sporosarcina saromensis M52 obtained from the sediment samples in Xiamen,to locate the Cr(Ⅵ) reduetase, and to study the effects of metal ions and small molecules on the reducing ability of Cr(Ⅵ) resisistant strain M52. Methods:The seed solution of M52 strain was inoculated into the LB medium containing different concentrations (0-600 mg·L^-1) of Cr(Ⅵ). After cultivating for 0-48 h, the absorbance (A) value of M52 strain liquid at 600 nm was measured by UV spectrophotometry. The growth of M52 strain in LB medium containing 0, 50, 100, 200, 400, and 600 mg·L^-1 Cr(Ⅵ) was observed. The intracellular and extracellular active substances obtained by centrifugation of M52 bacteria solution before and after sonication and the M52 in control group were cultured at 37℃ and pH 7.5, respectively. Using diphenylcarbazide spectrophotometry, the concentrations of Cr(Ⅵ) in the solution at 0, 12, 24, and 48 h were measured, and the reduction rates of Cr(Ⅵ) in intracellular and extracellular active substances at each time point were calculated. 0.2 mmol·L^-1 Mn²⁺, Fe²⁺ and Cu²⁺, 1 mmol·L^-1 SDS and 1% Triton X-100, Tween 80 were added to the LB medium as treatment groups, and the untreated LB liquid medium was used as control group. The seed solution was inoculated in treatment groups and control group at 4% concentration. The reduction rates of Cr(Ⅵ) by M52 at 0, 6, 12, 24, 36, and 48 h were calculated. The changes of the reduction rates of Cr(Ⅵ) by M52 in metal ion and small molecule treatment groups were investigated. Results:When the concentration of Cr(Ⅵ) was lower than 100 mg·L^-1, the growth of strain was promoted with the increase of concentration; when the concentration of Cr(Ⅵ) was higher than 100 mg·L^-1, the growth of the strain was inhibited with the increase of concentration; when the concentration of Cr(Ⅵ) was higher than 600 mg·L^-1, the M52 strain hardly grew. Compared with control group, the reduction rates of Cr(Ⅵ) by M52 occurred both inside and outside the cells were increased(P<0.05),and the intracellular Cr(Ⅵ) had the highest reduction rate. Compared with control group, the reduction rates of Cr(Ⅵ) by M52 were increased in the presence of Cu²⁺ and Fe²⁺ (P<0.05), and Cu²⁺ >Fe²⁺; the reduction rate was reduced in the presence of Mn²⁺ (P<0.05). Compared with control group, the reduction rates of Cr(Ⅵ) by M52 were reduced in the presence of small molecules SDS, Triton X-100, and Tween 80, and SDS > Triton X-100 > Tween 80. Conclusion:Low concentration of Cr(Ⅵ) can promote the growth of the M52 strain,and high concentration of Cr(Ⅵ) can inhibit the growth of the strain. The reduction of Cr(Ⅵ) by M52 mainly occurs in the cells. Cu²⁺ and Fe²⁺ can promote the reduction of Cr(Ⅵ) by M52.Tween 80, Triton X-100, and SDS can inhibit the reduction of Cr(Ⅵ) by M52.

Key words: Sporosarcina saromensis M52, hexavalent chromium, reductase, small molecules, metal ions