Biosynthesis of novel copolyesters containing 3-hydroxypivalic acid by Rhodococcus ruber NCIMB 40126 and related bacteria

Rhodococcus ruber and related Gram-positive bacteria synthesized and accumulated novel copolyesters containing 3-hydroxypivalic acid as constituent if the cells were cultivated in a mineral salts medium containing 3-hydroxypivalic acid and glucose as carbon sources. The copolyesters contributed 0.4–10% of the cellular dry mass, and they contained up to 78 mol% of 3-hydroxypivalic acid in addition to 3-hydroxybutyric acid and 3-hydroxyvaleric acid; a homopolyester of 3-hydroxypivalic acid was also synthesized under certain conditions. The presence of 3-hydroxypivalic acid in the accumulated copolyesters was confirmed by nuclear magnetic resonance spectrometry as well by coupled gas chromatography/mass spectrometry. This is the first time that the incorporation of 3-hydroxypivalic acid and therefore of a hydroxyalkanoic acid with two methyl group substituents at the α-carbon atom in a naturally occurring copolyester is reported. It indicates that 3-hydroxypivalic acid-coenzyme A is accepted by polyhydroxyalkanoic acid synthase as a substrate.