Constant fed-batch cultivation with glucose and propionate as co-substrate: A strategy to fine-tune...

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_even/odd) 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_odd 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_odd varied between 0.36 and 0.53 mol·mol^-1 (Y_HAodd/prop.), which are significantly lower than the theoretical maximum efficiency (1.0 mol·mol^-1). 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.