The seed solution of the S52 strain was inoculated and cultured overnight in LB medium. The extracellular active substance obtained by centrifugal filtration of the bacterial solution， the intracellular active substance obtained by ultrasonic ice-breaking bacteria and the S52 whole bacterial solution were added to the LB medium containing 50 mg·L^－1 Cr（Ⅵ） and cultured at 37 ℃， pH 8.0. Benzyl dihydrazide spectrophotometry was used to determine the Cr （Ⅵ） concentrations in the solution at 0， 3， 6，12， 24 and 48 h， and then the reduction rates of Cr（Ⅵ）， the relative activities and relative stabilities of intracellular and extracellular enzymes were calculated. Using a multi-factor mixed experiment design， the temperatures were set as 25 ℃， 30 ℃， 35 ℃， 40 ℃， 45 ℃， 50 ℃， and the pH values were 5.0， 6.0， 7.0， 8.0， 9.0， 10.0； the reduction rates of Cr（Ⅵ） by reductases at 0， 3， 6 and 12 h were calculated， then the effects of different temperatures and pH values on the reduction rate of reductase were analyzed， and the optimal reduction conditions were optimized. 0.2 mmol·L^－1 Cu²⁺， Mn²⁺ and Cd²⁺ solution， 1mmol·L^－1 SDS and EDTA， 1% Triton X-100， Tween 80 were added to the medium separately as treatment groups， and the untreated culture medium was used as control group. They were reacted with 50 mg·L^－1 Cr（Ⅵ） for 3 h under the optimal reduction conditions. The reduction rates of Cr（Ⅵ） were measured and calculated， and the changes of reduction rates in different metal ions and small molecules treatment groups were compared.

At 3 h， the reduction rates of Cr（Ⅵ） by intracellular and extracellular enzymes reached the highest， and the reduction ability of intracellular enzymes was higher than that of extracellular enzymes （P<0.05）. When the temperature was constant and the pH value was from 5.0 to 6.0， the reduction rates of Cr（Ⅵ） by intracellular and extracellular enzymes were increased significantly； when the pH values were gradually increased， the reduction rates of Cr（Ⅵ） were decreased significantly. Under certain pH condition， with the increase of temperature， the intracellular enzyme reduction rates were gradually increased， and the extracellular enzyme reduction rates were decreased. The differences in reduction rates between different temperature and pH groups were statistically significant （P<0.05）， and the interaction between temperature and pH was significant （P<0.05）. Compared with control group， the enzymatic reduction rate in Cu²⁺ treatment group reached to 46.4% （P<0.05），the reduction rates in Cd²⁺ and Mn²⁺ treatment groups were decreased（P<0.05）； there was no statistically significant difference in the reduction rate of Cr（Ⅵ） between small molecular substance Triton X-100 and control group （P>0.05）， while the reduction rates of Cr（Ⅵ） in Tween 80， EDTA and SDS treatment groups were lower than that in control group（P<0.05）.

The Cr（Ⅵ） reductase of strain S52 can play a reducing role both inside and outside the cells， and the reducing effect of intracellular enzyme is stronger than that of extracellular enzyme. The optimal temperature of intracellular enzymes is 35 ℃－45 ℃， and the optimal pH value is 7.0； the optimal temperature of extracellular enzymes is 25 ℃－30 ℃， and the optimal value is 7.0. Different metal ions and small molecules have different effects on the activities of reductases.