Accumulation of poly[(R)-3-hydroxyalkanoates] in Pseudomonas oleovorans during growth with octanoate in continuous culture at different dilution rates

Pseudomonas oleovorans ATCC 29347 was grown in chemostat culture at differe nt dilution rates with mineral media varying in their ratios of octanoate t o ammonia (C-0/N-0 ratio). At all dilution rates tested, three distinct gro wth regimes were observed: (i) carbon limitation with NH4+ in excess at low C-0/N-0 ratios, (ii) purely nitrogen-limited growth conditions at high C-0 /N-0 ratios with residual octanoate in the culture supernatant, and (iii) a n intermediate zone of dual-nutrient-limited growth conditions where both t he concentration of octanoate and that of ammonia were very low. The dual-n utrient-limited growth zone shifted to higher C-0/N-0 ratios with decreasin g dilution rates, and the extension of the dual-nutrient-limited growth zon e,vas inversely proportional to the growth rate. The cells accumulated the storage compound medium-chain-length poly[(R)-3-hydroxyalkanoate] (mcl-PHA) during dual (C and N)-nutrient-limited and N-limited growth conditions. Wi thin the dual-nutrient-limited growth zone, the cellular mcl-PHA contents i ncreased when the C-0/N-0 ratio in the feed was increased, whereas the cell ular mel-PEW level was independent from the feed C-0/N-0 ratio during N-lim ited growth. The monomeric composition of the accumulated mcl-PHA was indep endent of both the dilution rate and the feed C-0/N-0 ratio and consisted o f 12 mol% 3-hydroxyhexanoic acid and 88 mol% 3-hydroxyoctanoic acid. Accumu lation of mcl-PHA led to an increase in the cellular CIN ratio and to chang es in elemental growth yields for nitrogen and carbon.