Synthesis of poly(3-hydroxyalkanoates) by mutant and recombinant Pseudomonas strains

We have studied the accumulation kinetics and physical characteristics of the poly(3-hydroxyalkanoates) (PHAs) formed by several Pseudomonas strains, mutants and recombinants. Although PHA synthesis generally begins only after an essential nutrient such as N, P, S or Mg becomes limiting, we have identified at least one strain (P. putida KT2442) that begins producing PHA during the exponential growth phase. This PHA is chemically and physically identical to that produced by P. oleovorans GPol, the strain in which we first identified PHA. Analysis of the PHA formed by a mutant strain defective in PHA degradation (P. oleovorans GPo500) revealed that the molecular mass (M(w)), the monomer composition and thermal characteristics were similar to that of the PHA of the wild-type parent strain P. oleovorans GPol. The pha locus of P. oleovorans encodes enzymes that are involved in PHA biosynthesis and degradation. It has been subcloned to study the two PHA polymerases separately in a PHA- mutant (GPp104) derived from P. putida KT2442. The recombinant strains accumulated lower PHA levels than the wild-type strains, and the M(w) of these polymers were lower than those produced by the wild-type P. oleovorans and parent strain. The monomer composition of the two PHAs formed by the two PHA polymerases differed, indicating that the PHA polymerases have different substrate specificities for the incorporation of 3-hydroxyoctanoate and 3-hydroxyhexanoate monomers into PHA. Despite these differences, the PHAs formed were essentially indistinguishable from wild-type PHAs with respect to their thermal characteristics

Formation of Polyesters by Pseudomonas oleovorans: Effect of Substrates on Formation and Composition of Poly-(R)-3-Hydroxyalkanoates and Poly-(R)-3-Hydroxyalkenoates

Pseudomonas oleovorans grows on C(6) to C(12)n-alkanes and 1-alkenes. These substrates are oxidized to the corresponding fatty acids, which are oxidized further via the β-oxidation pathway, yielding shorter fatty acids which have lost one or more C(2) units. P. oleovorans normally utilizes β-oxidation pathway intermediates for growth, but in this paper we show that the intermediate 3-hydroxy fatty acids can also be polymerized to intracellular poly-(R)-3-hydroxyalkanoates (PHAs) when the medium contains limiting amounts of essential elements, such as nitrogen. The monomer composition of these polyesters is a reflection of the substrates used for growth of P. oleovorans. The largest monomer found in PHAs always contained as many C atoms as did the n-alkane used as a substrate. Monomers which were shorter by one or more C(2) units were also observed. Thus, for C-even substrates, only C-even monomers were found, the smallest being (R)-3-hydroxyhexanoate. For C-odd substrates, only C-odd monomers were found, with (R)-3-hydroxyheptanoate as the smallest monomer. 1-Alkenes were also incorporated into PHAs, albeit less efficiently and with lower yields than n-alkanes. These PHAs contained both saturated and unsaturated monomers, apparently because the 1-alkene substrates could be oxidized to carboxylic acids at either the saturated or the unsaturated ends. Up to 55% of the PHA monomers contained terminal double bonds when P. oleovorans was grown on 1-alkenes. The degree of unsaturation of PHAs could be modulated by varying the ratio of alkenes to alkanes in the growth medium. Since 1-alkenes were also shortened before being polymerized, as was the case for n-alkanes, copolymers which varied with respect to both monomer chain length and the percentage of terminal double bonds were formed during nitrogen-limited growth of P. oleovorans on 1-alkenes. Such polymers are expected to be useful for future chemical modifications