Microaerophilic environments improve the productivity of medium chain length polyhydroxyalkanoate biosynthesis from fatty acids in Pseudomonas putida LS46

Medium chain length polyhydroxyalkanoate (mcl-PHA, a commercially desirable biopolymer) synthesis from fatty acids is an oxidative process. Growth and mcl-PHA synthesis were studied in Pseudomonas putida LS46 when subjected to a spectrum of oxygen transfer rates, which were intended to simulate dissolved oxygen (DO) gradients likely to be encountered during process scale-up. It was found that maintaining DO at 1-5% (of air saturation at 30 degrees C) initiated significant mcl-PHA synthesis and concurrent growth at < 0.5 mu(max) was also observed. Further reductions in DO resulted in nearly negligible growth, but improved biopolymer synthesis. When the volumetric oxygen mass transfer coefficient (k(L)a) was reduced to 38 h(-1), DO was below detectable limits and both the biopolymer content (57.3 +/- 3.8% CDM) and yield (0.62 +/- 0.06 g mcl-PHA g octanoic acid(-1)) reached the maximum observed values. Under these conditions, the maximum rate of polymer synthesis was also observed (227.9 +/- 9.8 mg PHA g residual cell mass(-1) h(-1)), and this value was higher than that which could be achieved using nitrogen limitation. Further reductions in oxygen transfer rate did not improve productivity, and PHA synthesis completely ceased when aeration was replaced with N-2 gassing. These results suggest that manipulation of the bioreactor oxygen transfer rate during the PHA accumulation phase could be a strategy used to improve overall productivity during a fed batch or continuous feed process.