Journal of Bacteriology, December 1998, p. 6459-6467, Vol. 180, No. 24
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Polymer Chemistry Laboratory and the RIKEN Group of Japan Science and Technology Corporation, The Institute of Physical and Chemical Research (RIKEN), 2-1 Hirosawa, Wako-shi, Saitama 351-0198, Japan
Received 5 June 1998/Accepted 1 October 1998
Two types of polyhydroxyalkanoate (PHA) biosynthesis gene loci
(phb and pha) of Pseudomonas sp.
strain 61-3, which produces a blend of poly(3-hydroxybutyrate)
[P(3HB)] homopolymer and a random copolymer
{poly(3-hydroxybutyrate-co-3-hydroxyalkanoate) [P(3HB-co-3HA]} consisting of 3HA units of 4 to 12 carbon atoms, were cloned and analyzed at the molecular level. In the
phb locus, three open reading frames encoding
polyhydroxybutyrate (PHB) synthase (PhbCPs),
-ketothiolase (PhbAPs), and NADPH-dependent acetoacetyl coenzyme A reductase (PhbBPs) were found. The genetic
organization showed a putative promoter region, followed by
phbBPs-phbAPs-phbCPs. Upstream from phbBPs was found the
phbRPs gene, which exhibits significant
similarity to members of the AraC/XylS family of transcriptional activators. The phbRPs gene was found to be
transcribed in the opposite direction from the three structural genes.
Cloning of phbRPs in a relatively high-copy
vector in Pseudomonas sp. strain 61-3 elevated the levels
of
-galactosidase activity from a transcriptional phb
promoter-lacZ fusion and also enhanced the 3HB fraction in the polyesters synthesized by this strain, suggesting that
PhbRPs is a positive regulatory protein controlling the
transcription of phbBACPs in this bacterium. In
the pha locus, two genes encoding PHA synthases
(PhaC1Ps and PhaC2Ps) were flanked by a PHA
depolymerase gene (phaZPs), and two adjacent
open reading frames (ORF1 and phaDPs), and the
gene order was ORF1, phaC1Ps,
phaZPs, phaC2Ps, and
phaDPs. Heterologous expression of the cloned
fragments in PHA-negative mutants of Pseudomonas putida and
Ralstonia eutropha revealed that PHB synthase and two PHA
synthases of Pseudomonas sp. strain 61-3 were specific for
short chain length and both short and medium chain length 3HA units, respectively.
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