Accumulation of Poly[(R)-3-Hydroxyalkanoates] in Pseudomonas oleovorans during Growth with Octanoate in Continuous Culture at Different Dilution Rates

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American Society for Microbiology

RESUMO

Pseudomonas oleovorans ATCC 29347 was grown in chemostat culture at different dilution rates with mineral media varying in their ratios of octanoate to ammonia (C0/N0 ratio). At all dilution rates tested, three distinct growth regimes were observed: (i) carbon limitation with NH4+ in excess at low C0/N0 ratios, (ii) purely nitrogen-limited growth conditions at high C0/N0 ratios with residual octanoate in the culture supernatant, and (iii) an intermediate zone of dual-nutrient-limited growth conditions where both the concentration of octanoate and that of ammonia were very low. The dual-nutrient-limited growth zone shifted to higher C0/N0 ratios with decreasing dilution rates, and the extension of the dual-nutrient-limited growth zone was 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. Within the dual-nutrient-limited growth zone, the cellular mcl-PHA contents increased when the C0/N0 ratio in the feed was increased, whereas the cellular mcl-PHA level was independent from the feed C0/N0 ratio during N-limited growth. The monomeric composition of the accumulated mcl-PHA was independent of both the dilution rate and the feed C0/N0 ratio and consisted of 12 mol% 3-hydroxyhexanoic acid and 88 mol% 3-hydroxyoctanoic acid. Accumulation of mcl-PHA led to an increase in the cellular C/N ratio and to changes in elemental growth yields for nitrogen and carbon.

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