EXPRESSION OF POLYHYDROXYALKANOIC-ACID-BIOSYNTHESIS GENES IN METHYLOTROPHIC BACTERIA RELYING ON THE RIBULOSE MONOPHOSPHATE PATHWAY

Four representatives of methylotrophic bacteria relying on the ribulos e monophosphate (RMP) pathway were investigated for their capability t o synthesize polyhydroxyalkanoic acids (PHA). In Methylophilus methylo trophus B115, Methylobacillus glycogenes strains B121 and B53 and Acet obacter methanolicus B58 no beta-ketothiolase, acetoacetyl-coenzyme A (CoA) reductase or PHA synthase could be detected, and hybridization e xperiments using heterologous DNA probes derived from PHA-biosynthesis genes of Methylobacterium extorquens or Alcaligenes eutrophus gave no evidence for the presence of the corresponding genes in these PHA-neg ative methylotrophic bacteria. Fragments harbouring a cluster of PHA-b iosynthesis genes of A. eutrophus or Chromatium vinosum or isolated PH A synthase structural genes of M extorquens, Rhodospirillum rubrum or Rhodobacter sphaeroides were mobilized into the RMP pathway bacteria m entioned above. Only transconjugants, which harboured the PHA-biosynth esis genes of A. eutrophus or C. vinosum, expressed active beta-ketoth iolase, acetoacetyl-CoA reductase and PHA synthase and accumulated pol y(3-hydroxybutyric acid) (PHB). Highest amounts of PHB (up to 15% of t he cellular dry weight) were accumulated in transconjugants of Methylo philus methylotrophus B115 or of Methylobacillus glycogenes strains B1 21 and B53 harbouring the PHA-biosynthesis genes of C. vinosum.