Stress fermentation strategies for the production of hyperthermostable superoxide dismutase from Thermus thermophilus HB27: Effects of ions
Zhu H., Liu J., Qu J., Gao X., Pan T., Cui Z., Zhao X., Lu JR.
In this study, we explored how ammonium and metal ion stresses affected the production of recombinant hyperthermostable manganese superoxide dismutase (Mn-SOD). To improve Mn-SOD production, fed-batch culture in shake flasks and bioreactor fermentation were undertaken to examine the effects of NH4+ and Mn2+ feeding. Under the optimized feeding time and concentrations of NH4+ and Mn2+, the maximal SOD activity obtained from bioreactor fermentation reached some 480 U/ml, over 4 times higher than that in batch cultivation (113 U/ml), indicating a major enhancement of the concentration of Mn-SOD in the scale-up of hyperthermostable Mn-SOD production. In contrast, when the fed-batch culture with appropriate NH4+ and Mn2+ feeding was carried out in the same 5-L stirred tank bioreactor, a maximal SOD concentration of some 450 U/ml was obtained, again indicating substantial increase in SOD activity as a result of NH4+ and Mn2+ feeding. The isoelectric point (pI) of the sample was found to be 6.2. It was highly stable at 90 °C and circular dichroism measurements indicated a high α-helical content of 70 % as well, consistent with known SOD properties. This study indicates that NH4+ and Mn2+ play important roles in Mn-SOD expression. Stress fermentation strategies established in this study are useful for large-scale efficient production of hyperthermostable Mn-SOD and may also be valuable for the scale-up of other extremozymes. © 2013 Springer Japan.