Enhanced production of poly-3-hydroxybutyrate by recombinant Escherichia coli containing NAD kinase and phbCAB operon

Techniques for chromosomal integration and expression optimization in Escherichia coli

Due to the inherent expression stability and low metabolic burden to the host cell, the expression of heterologous proteins in the bacterial chromosome in a precise and efficient manner is highly desirable for metabolic engineering and live bacterial applications. However, obtaining suitable chromosome expression levels is particularly challenging. In this minireview, we briefly present the technologies available for the integration of heterologous genes into Escherichia coli chromosomes and strategies to optimize the expression levels of heterologous proteins.

NADPH supply for poly(3-hydroxybutyrate) synthesis concomitant with enzymatic oxidation of phosphite

Acetoacetyl-CoA reductase (PhaB), involved in poly(3-hydroxybutyrate) [P(3HB)] biosynthesis, requires the coenzyme NADPH as a reducing agent. In this study, the effect of NADPH supply on P(3HB) production was investigated in vitro and in vivo using a phosphite dehydrogenase double mutant (PtxD_EAAR), which catalyzes oxidation of phosphite to phosphate with the generation of NADH and NADPH. In an in vitro assay using purified enzymes, P(3HB) polymerization was observed only when phosphite and PtxD_EAAR were present, confirming that NADPH was supplied to PhaB. In an in vivo assay using Escherichia coli as a production host for P(3HB), the presence of phosphite and PtxD_EAAR did not influence the yield of P(3HB) under normal growth conditions. However, P(3HB) yield increased 3.2-fold in non-growing E. coli cells compared to the control, suggesting that PtxD_EAAR-mediated NADPH generation is coupled with P(3HB) biosynthesis. This study confirmed the use of PtxD_EAAR for supplying NADPH during P(3HB) synthesis in vitro and in vivo.