Production of poly(β‐hydroxyalkanoates) with β‐substituents containing terminal ester groups by Pseudomonas oleovorans

Pseudomonas oleovorans was grown separately on the methyl, ethyl and tert ‐butyl esters of octanoic, nonanoic and decanoic acid in attempts to obtain poly(β‐hydroxyalkanoates), PHAs, with ester groups at the terminal position of the β‐substituent. The growth rate increased from methyl to tert ‐butyl esters, but the rate for the slowest growing substrates, the methyl esters, could be accelerated by using special feeding techniques, either by prefeeding with sodium acetate or by cofeeding with a good growth and polymer producing substrate, sodium octanoate. For the ethyl esters the prefeeding technique had minimal success, but a considerable increase of the growth rate was achieved by starting the bacterial growth with a pre‐culture that was grown on the substrate under investigation. Tert ‐butyl nonanoate as the substrate gave the most rapid growth, but the growth rate was not influenced by special feeding techniques. All of these substrates formed copolymers which contained up to eight different repeating units and some had terminal ester groups on alkane side chains of varying lengths. The use of methyl esters as substrates resulted in the incorporation of a reasonably high degree of pendant methyl ester groups in the polymer produced, and the amount of repeating units carrying pendant ester groups dependend directly on the oxygen supply available to the bacterial culture. The fermentation of substrates with ethyl ester groups resulted in the formation of copolymers containing either unsubstituted units or units containing either ethyl or methyl ester groups, or both. The reason for this unexpected behavior was not clarified. The large tert ‐butyl ester group was not maintained as a substituent group in the polymer, but instead, growth on this substrate always resulted in producing polymers consisting of the unsubstituted repeating units expected from the corresponding carboxylic acid alone.