Continuous production of long-side-chain poly-β-hydroxyalkanoates by Pseudomonas oleovorans

Abstract

Shake flask experiments showed that Pseudomouas 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 C4/C6/C8/C10 ratio of 0.1:1.7:20.7:1.0. At μ > 0.3 h-1, a decrease in the percentage of C8 with a concomitant increase in C10 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 NH4+ 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.