FORMATION OF POLY(3-HYDROXYBUTYRATE-CO-3-HYDROXYHEXANOATE) BY PHA SYNTHASE FROM RALSTONIA-EUTROPHA

The acetoacetyl-CoA reductase and the polyhydroxyalkanoate (PHA) synth ase from Ralstonia eutropha (formerly Alcaligenes eutrophus) were expr essed in Escherichia coli, Klebsiella aerogenes, and PHA-negative muta nts of R. eutropha and Pseudomonas putida. While expression in E. coli strains resulted in the accumulation of poly(3-hydroxybutyrate) [PHB] , strains of R. eutropha, P. putida and K. aerogenes accumulated poly( 3-hydroxybutyrate-co-3-hydroxyhexanoate) [poly(3HB-co-3HHx)] when even chain fatty acids were provided as carbon source, and poly(3-hydroxyb utyrate-co-3-hydroxyvalerate) [poly(3HB-co-3HV)] when odd chain fatty acids were provided as carbon source. This suggests that fatty acid de gradation can be directly accessed employing only the acetoacetyl-CoA reductase and the PHA synthase. This is also the first proof that the PHA synthase from R. eutropha can incorporate 3-hydroxyhexanoate (3HHx ) into PHA and has, therefore, a broader substrate specificity than pr eviously described. (C) 1998 Elsevier Science B.V. All rights reserved .