Metabolic engineering of Halomonas bluephagenesis to metabolize xylose for poly-3-hydroxybutyrate production

Halomonas bluephagenesis is an essential host for next generation industrial biotechnology (NGIB) due to its ability to grow under high-salt and alkali conditions. In this study, H. bluephagenesis TD01 was engineered to metabolize xylose. Firstly, four different xylose-specific transporters were introduced yet xylose cannot be consumed. Further expression of xylose isomerase from Escherichia coli enabled cell growth on xylose and poly-3-hydroxybutyrate (PHB) accumulation of 0.39 g/L. Additional overexpression of xylulose kinase to direct carbon flux into pentose phosphate pathway decreased PHB production. Subsequently, the ribulose-1-phosphate pathway was constructed by introducing enzymes including D-tagatose-3-epimerase, fuculokinase, and fuculose-phosphate aldolase. The recombinant strain reached 2.09 g/L cell dry weight with 0.87 g/L PHB pro-duction. Finally, another carbon-efficient phosphoketolase pathway was introduced through the overexpression of exogenous phosphoketolase, which improved cell dry weight and PHB titer to 8.81 g/L and 5.37 g/L, respectively. This is the first report on xylose utilization by H. bluephagenesis and would provide helpful engi-neering strategies for the industrial polyhydroxyalkanoate production using xylose.