Enhancement of medium-chain-length polyhydroxyalkanoates biosynthesis from glucose by metabolic engineering in Pseudomonas mendocina

Objectives To enhance the biosynthesis of medium-chain-length polyhydroxyalkanoates (PHA MCL ) from glucose in Pseudomonas mendocina NK-01, metabolic engineering strategies were used to block or enhance related pathways. Results Pseudomonas mendocina NK-01 produces PHA MCL from glucose. Besides the alginate oligosaccharide biosynthetic pathway proved by our previous study, UDP- d -glucose and dTDP- l -rhamnose biosynthetic pathways were identified. These might compete for glucose with the PHA MCL biosynthesis. First, the alg operon, galU and rmlC gene were deleted one by one, resulting in NK-U-1(∆ alg ), NK-U-2 (∆ alg ∆ galU ), NK-U-3( alg ∆ galU ∆ rmlC ). After fermentation for 36 h, the cell dry weight (CDW) and PHA MCL production of these strains were determined. Compared with NK-U: 1) NK-U-1 produced elevated CDW (from 3.19 ± 0.16 to 3.5 ± 0.11 g/l) and equal PHA MCL (from 0.78 ± 0.06 to 0.79 ± 0.07 g/l); 2) NK-U-2 produced more CDW (from 3.19 ± 0.16 to 3.55 ± 0.23 g/l) and PHA MCL (from 0.78 ± 0.06 to 1.05 ± 0.07 g/l); 3) CDW and PHA MCL dramatically decreased in NK-U-3 (1.53 ± 0.21 and 0.41 ± 0.09 g/l, respectively). Additionally, the phaG gene was overexpressed in strain NK-U-2. Although CDW of NK-U-2/ phaG decreased to 1.29 ± 0.2 g/l, PHA titer (%CDW) significantly increased from 24.5 % up to 51.2 %. Conclusion The PHA MCL biosynthetic pathway was enhanced by blocking branched metabolic pathways in combination with overexpressing phaG gene.