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Strains of two types of methylotrophic bacteria, Paracoccus denitrificans and Methylobacterium extorquens, synthesized the copolyester poly(3-hydroxybutyrate-co-3-hydroxyvalerate) when methanol and n -amyl alcohol were added together to nitrogen-limited medium. The composition of the copolyester differed considerably between the two strains: the copolyester from P. denitrificans was comparatively rich in 3-hydroxyvalerate (3HV). The 3HV content of the copolyester synthesized by this strain increased with increasing concentrations of n -amyl alcohol. Its maximum content was 91.5 mol% under the conditions used. In M. extorquens, the maximum 3HV content was limited to 38.2 mol%. Since n -amyl alcohol served as a substrate for a standard methanol dehydrogenase, the enzyme was proposed to oxidize both methanol and n -amyl alcohol in the first step of copolyester synthesis from these substrates by methanol-grown cells.