Abstract
SummaryCpxR is a global response regulator that negatively influences the antimicrobial activities of Xenorhabdus nematophila. Herein, the wildtype and ΔcpxR mutant of X. nematophila were cultured in a 5‐l and 70‐l bioreactor. The kinetic analysis showed that ΔcpxR significantly increased the cell biomass and antibiotic activity. The maximum dry cell weight (DCW) and antibiotic activity of ΔcpxR were 20.77 ± 1.56 g L−1 and 492.0 ± 31.2 U ml−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 ΔcpxR, where ΔcpxR was sensitive to alkaline pH conditions. The optimal cell growth and antibiotic activity of ΔcpxR 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 ΔcpxR considerably increased the biomass of X. nematophila at a late stage of fermentation. In addition, ΔcpxR significantly promoted the biosynthesis of Xcns but decreased the production of nematophin.
Highlights
Xenorhabdus nematophila is a unique Gram-negative bacterium that develops a mutualistic association with an infective dauer juvenile (IJ) insect-pathogenic nematode in the genus of Steinernema (Thomas and Poinar, 1979)
The maximum dry cell weight (DCW) and antibiotic activity of DcpxR were 20.77 Æ 1.56 g LÀ1 and 492.0 Æ 31.2 U mlÀ1 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%
Summary
Xenorhabdus nematophila is a unique Gram-negative bacterium that develops a mutualistic association with an infective dauer juvenile (IJ) insect-pathogenic nematode in the genus of Steinernema (Thomas and Poinar, 1979). X. nematophila has been known to produce several secondary metabolites, including indole derivatives (Paul et al, 1981; Sundar and Chang, 1993; Li et al, 1995), nematophin (Li et al, 1997), insecticidal proteins (Morgan et al, 2001; Sergeant et al, 2003; Yang et al, 2009; Sheets et al, 2011; Hinchliffe, 2010), benzylideneacetone (Ji et al, 2004), xenocoumacins (Xcns) (McInerney et al, 1991) and the major class of non-ribosomal produced secondary metabolites (Crawford et al, 2011). These metabolites display a wide range of bioactivities with potential interest for pharmaceutical, agricultural and chemical applications. These naturally occurring antibiotics and their derivatives may provide beneficial leads in the future research and manufacturing of agrochemicals
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