Constant fed-batch cultivation with glucose and propionate as co-substrate: A strategy to fine-tune polyhydroxyalkanoates monomeric composition in Pseudomonas spp.

Pseudomonas sp. LFM693 is a 2-methylisocitrate lyase (prpB) disrupted mutant. This enzyme catalyzes a step in the 2-methylcitrate cycle, the only known and described pathway for propionate oxidation in this organism. The affected mutants can efficiently produce PHA containing even and odd-chain length hydroxyalkanoates (HA) in the presence of propionate and glucose. In this study, a constant fed-batch configuration was utilized to control the composition of PHA and decrease the toxicity of propionate. The incorporation of HA into the copolymer was linear, ranging from 7 to approximately 30 %, and correlated directly with the propionate/glucose molar ratio in the feeding solution. This allowed for the molecular composition of the mclPHA to be fine-tuned with minimum process monitoring and control. The average PHA content was 52 % cell dry weight with a molar composition that favored 3-hydroxyalkanoates containing C8, C9, and C10. The conversion factor of propionate to HA varied between 0.36 and 0.53 mol·mol (Y.), which are significantly lower than the theoretical maximum efficiency (1.0 mol·mol). These results along with the lack of 2-methylisocitrate as a byproduct provides further support for the evidence that the mutant prpB is still capable of oxidizing propionate.