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

Abstract

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.