Isolation and characterization of a transposon mutant of Pseudomonas fluorescens BM07 enhancing the production of polyhydroxyalkanoic acid but deficient in cold-induced exobiopolymer production.

Pseudomonas fluorescens BM07 is known to produce cold-induced exobiopolymer, which is mainly composed of water-insoluble hydrophobic polypeptides (up to 85%) and saccharides (8%), by decreasing the culture temperature down to as low as 10 degrees C. We screened for transposon insertion mutants of P. fluorescens BM07 that were unable to produce the exobiopolymer. Among the eight mutants that showed the deficiency of exobiopolymer and O-lipopolysaccharide, one mutant BM07-59 that had the highest polyhydroxyalkanoates (PHA) production was selected. The transposon inserted gene in BM07-59 was identified as galU. The disruption of the gene galU coded for the putative product, UDP-glucose pyrophosphorylase (GalU), resulted in 1.5-fold more accumulation of PHA compared with the wild-type strain from 70 mM fructose or galactose at 30 degrees C. Electrophoretic analysis of lipopolysaccharide showed that the mutant lacked the O-antigen lipopolysaccharide bands. The glycosyl composition of the lipopolysaccharide produced by the mutant strain was significantly different from that of the wild-type strain. We suggest that the deletion of galU could be a way to shift carbon flux efficiently from exobiopolymer toward PHA in P. fluorescens BM07.