Improving polyhydroxyalkanoate production by knocking out the genes involved in exopolysaccharide biosynthesis in Haloferax mediterranei.

Haloferax mediterranei is capable of producing large amounts of poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV) from many kinds of carbon sources, with exopolysaccharide (EPS) as a by-product. In this study, we identified a gene cluster involved in EPS biosynthesis in H. mediterranei. Knocking out the genes in this cluster encoding the putative UDP-N-acetylglucosamine 6-dehydrogenase (HFX_2145), glycosyltransferases (HFX_2146 and HFX_2147) and polysaccharide transporter (HFX_2148) eliminated EPS synthesis. The deficiency in EPS biosynthesis in the mutant strain remarkably decreased the viscosity of culture broth, and hence increased the dissolved oxygen content and decreased the foaming propensity. Compared with the wild-type (WT) strain, the PHBV production of the EPS-mutant strain was significantly enhanced (approximately 20%), whereas the cell growth rate remained similar under the same culture conditions. These results indicated that the carbon sources used for synthesizing EPS were shifted to PHBV production. Thus, a novel engineered H. mediterranei strain was developed, which would be favorable for future industrial production of PHBV.