FIG. 4.

pha and phb operons. The loci encoding the genes for PHA formation have been characterized from 18 different species. Genes specifying enzymes for ssc-PHA formation are designated phb, and those specifying enzymes for msc-PHA formation are designated pha. Not all pathways have completely been elucidated in these strains. The emerging picture is that pha and phb genes are not necessarily clustered and that the gene organization varies from species to species. Other genes possibly related to PHA metabolism may be linked to the essential pha and phb genes. (A) Complete phbCAB operons. (B) Interrupted phb loci. (C) Incomplete phb loci. (D) phb loci from organisms that encode two subunit P(3HB) polymerases. (E) The phbCJ locus of A. caviae involved in P(3HB-3HH) formation. (F) pha loci for msc-PHA formation in Pseudomonas.