IPTG‐induced high protein expression for whole‐cell biosynthesis of L‐phosphinothricin

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Abstract
Background: Biocatalytic production of L‐phosphinothricin (L‐PPT) is currently the most promising method. In this work, we use an Escherichia coli strain coexpressing of D‐amino acid oxidase and catalase (E. coli DAAO‐CAT) to oxidation biocatalytic D‐PPT to PPO, then use the second E. coli strain coexpressing glutamate dehydrogenase and formate dehydrogenase (E. coli GluDH‐FDH) to reduce biocatalytic PPO to L‐PPT.Main Methods and Major Results: We compared the effects of different concentrations of IPTG or lactose on protein expression and enzyme activity in 5 L fermenter. The best induction conditions for E. coli DAAO‐CAT were 0.05 mM IPTG, induction for 18 h at 28°C. The specific enzyme activities of DAAO and CAT were 153.20 U g−1 and 896.23 U g−1, respectively. The optimal induction conditions for E. coli GluDH‐FDH were 0.2 mM IPTG, induction for 19 h at 28°C. The specific enzyme activities of GluDH and FDH were 41.72 U g−1 and 109.70 U g−1, respectively. The 200 mM D‐PPT was biocatalyzed by E. coli DAAO‐CAT for 4 h with space‐time yield of 9.0 g·L−1·h−1 and conversion rate of over 99.0%. Then 220 mM PPO was converted to L‐PPT by E. coli GluDH‐FDH for 3 h with space‐time yield of 14.5 g·L−1·h−1 and conversion rate of over 99.0%. To our knowledge, this is the most efficient biocatalytic reaction for L‐PPT production.Conclusions and Implications: We found that IPTG has advantages compared with lactose in the enzyme activity and biomass of E. coli DAAO‐CAT and E. coli GluDH‐FDH, and IPTG is more environmentally friendly. Our data implicated that IPTG can replace lactose in terms of economic feasibility and effectiveness for scaled‐up industrial fermentations.

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