Effects of cpxR on the growth characteristics and antibiotic production of Xenorhabdus nematophila

CpxR is a global response regulator that negatively influences the antimicrobial activities of Xenorhabdus nematophila. Herein, the wildtype and cpxR mutant of X. nematophila were cultured in a 5-l and 70-l bioreactor. The kinetic analysis showed that cpxR significantly increased the cell biomass and antibiotic activity. The maximum dry cell weight (DCW) and antibiotic activity of cpxR were 20.77 +/- 1.56gL(-1) and 492.0 +/- 31.2Uml(-1) and increased by 17.28 and 97.33% compared to the wildtype respectively. Xenocoumacin 1 (Xcn1), a major antimicrobial compound, was increased 3.07-fold, but nematophin was decreased by 48.7%. In 70-l bioreactor, DCW was increased by 18.97%, while antibiotic activity and Xcn1 were decreased by 27.71% and 11.0% compared to that in 5-l bioreactor respectively. Notably, pH had remarkable effects on the cell biomass and antibiotic activity of cpxR, where cpxR was sensitive to alkaline pH conditions. The optimal cell growth and antibiotic activity of cpxR occurred at pH 7.0, while Xcn1 was increased 5.45- and 3.87-fold relative to that at pH 5.5 and 8.5 respectively. These findings confirmed that cpxR considerably increased the biomass of X. nematophila at a late stage of fermentation. In addition, cpxR significantly promoted the biosynthesis of Xcns but decreased the production of nematophin.