Optimization of phenazine-1-carboxylic acid production by a gacA/qscR-inactivated Pseudomonas sp. M18GQ harboring pME6032Phz using response surface methodology.

Phenazine-1-carboxylic acid (PCA) production was enhanced in Pseudomonas sp. M18 wild strain and its mutants carrying recombinant pME6032Phz for phz gene cluster overexpression, among which Pseudomonas sp. strain M18GQ/pME6032Phz, a gacA and qscR double gene chromosomally inactivated mutant harboring pME6032Phz, showed the highest PCA yield. The conditions for fermentation and isopropyl-beta-D-1-thiogalactopyranoside (IPTG) induction were optimized for strain M18GQ/pME6032Phz in shake flask experiments. A one-factor-at-a-time approach, followed by a fractional factorial design identified soybean meal, corn steep liquor, and ethanol as statistically significant factors. Optimal concentrations and mutual interactions of the factors were then determined by the method of steepest ascent and by response surface methodology based on the center composite design. The predicted PCA production was 6,335.2 mg/l after 60 h fermentation in the optimal medium of 65.02 g soybean meal, 15.36 g corn steep liquor, 12 g glucose, 21.70 ml ethanol, and 1 g MgSO(4) per liter in the flask fermentations, with induction of 1.0 mmol/l IPTG 24 h after inoculation. In an experimental validation under these conditions, the maximum PCA production was 6,365.0 mg/l. This represents a approximately 60% increase over production by strain M18GQ in optimal conditions. The negative effect of plasmid pME6032 on the expression of chromosomally located phz gene cluster was found in Pseudomonas sp. M18GQ, and the possible reason was discussed in the text.