Effect of Zn²⁺ on halohydrin dehalogenase expression and accumulation through multi-parameter correlation research...

Using 5 Zn²⁺ supplementation strategies in a 50 L batch bioreactor named FUS-50L(A), possible correlations among Zn²⁺ content and addition timing, physiologic activity (PA), halohydrin dehalogenase (HheC) accumulation of Escherichia coli P84A/MC1061 were systematically investigated. First, Zn²⁺ was confirmed as the significant factor, and its optimal concentration for HheC expression was 3.87 mg/L through fermentation experiments in shaking flasks. Second, based on experimental results from the different strategies, it was found that PA, nutrient consumption rate (NCR) and specific growth rate (μ) for E. coli P84A/MC1061 were promoted in the log phase (4-8 h) under appropriate Zn²⁺ concentrations in the lag phase and late log phase. Furthermore cell biomass was also increased to a higher level and the maximum HheC activity (i.e. HheC_max) was increased by 9.80%, and the time to reach HheC_max was reduced from 16 to 12 hours. Furthermore, appropriate supplementation of Zn²⁺ caused higher μ for E. coli P84A/MC1061, which resulted in more rapid accumulation of increased acetic acid concentrations, leading to higher acetic acid consumption avoiding any negative effects on producing HheC because of carbon source being exhausted prematurely and acetic acid being consumed rapidly.