Continuous Production of Long-Side-Chain Poly-β-Hydroxyalkanoates by Pseudomonas oleovorans

Abstract

Shake flask experiments showed that Pseudomonas oleovorans began to be growth inhibited at 4.65 g of sodium octanoate liter -1 , with total inhibition at 6 g liter -1 . In chemostat studies with 2 g of ammonium sulfate and 8 g of octanoate liter -1 in the feed, the maximum specific growth rate was 0.51 h -1 , and the maximum specific rate of poly-β-hydroxyalkanoate (PHA) production was 0.074 g of PHA g of cellular protein -1 h -1 at a dilution rate ( D ) of 0.25 h -1 . When the specific growth rate (μ) was <0.3 h -1 , the PHA composition was relatively constant with a C 4 /C 6 /C 8 /C 10 ratio of 0.1:1.7:20.7:1.0. At μ > 0.3 h -1 , a decrease in the percentage of C 8 with a concomitant increase in C 10 monomers as μ increased was probably due to the effects of higher concentrations of unmetabolized octanoate in the fermentor. At D = 0.24 h -1 and an increasing carbon/nitrogen ratio, the percentage of PHA in the biomass was constant at 13% (wt/wt), indicating that nitrogen limitation did not affect PHA accumulation. Under carbon-limited conditions, the yield of biomass from substrate was 0.76 g of biomass g of octanoate -1 consumed, the yield of PHA was 0.085 g of PHA g of octanoate -1 used, and 7.9 g of octanoate was consumed for each gram of NH 4 + supplied. The maintenance coefficient was 0.046 g of octanoate g of biomass -1 h -1 . Replacement of sodium octanoate with octanoic acid appeared to result in transport-limited growth due to the water insolubility of the acid.