Batch-fermentation experiments showed that Herbaspirillum seropedicae Z69 was able to accumulate up to 36% of its biomass as PHB when grown on glucose as a carbon source. Accumulation of PHB paralleled entry of the bacteria into the stationary phase of growth. When grown on nonanoic acid as a sole carbon source H. seropedicae accumulated poly(3-hydroxybutyrate-co-3-hydroxyvalerate), P(3HB-co-3HV) with a relative abundance of 2:1 for the 3HB and 3HV monomers, respectively. Enzymatic activity specifying PHB biosynthesis, i.e., beta-ketothiolase and acetoacetyl-CoA reductase (NADPH) were found in cell-free extracts of strains Z67 and Z69. To enable H. seropedicae to grow on lactose, a recombinant H. seropedicae strain, Z69 (pHM3) expressing the Escherichia coli lacZ lacY genes was constructed. H. seropedicae Z69 (pHM3) grown on lactose as a sole carbon source accumulated up to 36% of its biomass as PHB. (c) 2006 Elsevier Inc. All rights reserved.