Effect of C/N Ratio on the Production of Poly(3-hydroxyalkanoates) by the Methylotroph Paracoccus denitrificans

Two series of carbon sources, linear primary C₁∼C₉ alcohols and linear C₂∼C₁₀ monocarboxylic acids were tested for PHA synthesis in Paracoccus denitrificans. The results showed that the growth-associated synthesis of PHA could be referred only to the carbon sources with odd number of carbon except methanol. For all carbon sources with even number of carbon, nitrogen limitation was required to induce PHA synthesis in P. denitrificans. Poly(3-hydroxyvalerate)[P(3HV)] homopolymer was synthesized from C₅, C₇and C₉ while growing in the presence of nitrogen, but the nitrogen depletion in the later growth period incorporated 3-hydroxybutyrate(3HB) unit into the polymer chain. The optimum C/N ratio for P (3HV) homopolymer production was found to be 10 when the strain was grown on 10 ml/1 of valeric acid for 96 h. P. denitrificans synthesized P(3HB-co-3HV) copolymers from n-hexanoic and n-octanoic acid. The microstructural characterics of the P(3HB-co-3HV) copolymer from n-propanol was investigated using ¹³C-nuclear magnetic resonance spectroscopy, showing a structural heterogeneity.