Production of PHAs from mixed and pure cultures of Pseudomonas sp. using short-chain fatty acids as carbon source under nitrogen limitation

An enriched culture of polyhydroxyalkanoates (PHAs)-forming bacteria was developed using activated sludge from a municipal wastewater treatment plant as inoculum. The culture was developed under alternating cycling between carbon and nitrogen limitation. After several cycles, the predominant bacteria were identified and it was shown that a consortium of Pseudomonas sp. had been formed. The PHAs production efficiency of the mixed culture was studied under nonaseptic, nitrogen limitation conditions, whereas two isolates were studied in terms of PHAs accumulation under both nitrogen limitation and simultaneous nitrogen- and oxygen-limiting conditions. A synthetic medium with volatile fatty acids (VFAs) was used in all cases as carbon source. The mixed culture led to better final yields of PHAs/VFAs consumed as well as faster accumulation rates. Regarding the effect of dissolved oxygen (DO) concentration, it was shown that PHAs production was strongly favored by the limiting conditions in isolate A, whereas isolate B did not seem to be affected.