Expression and activity of heterologous hydroxyisocaproate dehydrogenases in Synechocystissp. PCC 6803 ΔhoxYH

Exploiting light to drive redox reactions is currently a hot topic since light is considered as an environmentally friendly source of energy. Consequently, cyanobacteria, which can use light e.g., for generating NADPH, are in the focus of research. Previously, it has been shown that various heterologous redox enzymes could be expressed in these microorganisms. Here we demonstrated the successful inducer-free expression of α-keto-acid dehydrogenases (L-HicDH and D-HicDH) from Lactobacillus confususDSM 20196 and Lactobacillus paracaseiDSM 20008 in Synechocystissp. PCC 6803 ΔhoxYHmutant using replicative plasmids. While the L-HicDH showed poor activity limited by the amount of expressed enzyme, the D-HicDH was applied both in vivoand in vitro, transforming the selected α-keto acids to the corresponding optically pure (R)-α-hydroxy acids (ee>99%) in up to 53% and 90% conversion, respectively.