Yonghong Wang

College of Plant Protection, Northwest A&F University, Yangling 712100, P. R. China

Bacteria of the genera Xenorhabdus and Photorhabdus are entomopathogenic bacteria symbiotically associated with entomopathogenic nematodes belonging to the genera Steinernema and Heterorhabditis, respectively, and are pathogenic against different insect. In order to clarify the mechanism of CpxR regulates secondary metabolite production of X. nematophila. The ΔcpxR mutant strain was constructed by gene knockout technology. The differences between ΔcpxR and wild strain YL001 in the antimicrobial activity, biosynthesis gene expression of the major antimicrobial compounds in X. nematophila (XCNs and PAX), the gene expression of some regulators related to secondary metabolite production (EnvZ/OmpR and Lrp) and the production of the major antimicrobial compounds (XCNs) were analyzed. The results showed that ΔcpxR exhibited strong antimicrobial activity compared to the wild strain YL001 from in vitro to in vivo. RT-PCR analysis revealed that the level of mRNA expression for xcnA-L of ΔcpxR was increased compared to the wild strain YL001, but the expression of xcnM and xcnN were decreased. These finding were supported by qRT-PCR analysis showing that xcnA expression increased 1.8-fold while xcnM and xcnN expression decreased 0.600- and 0.800-fold at pH 8.5 compared the wild strain YL001. The expression level of major transcriptional regulators associated with antimicrobial activity envZ and ompR decreased 0.35- and 0.20-fold in ΔcpxR, however the expression level of lrp increased 2.80-fold in ΔcpxR compared that in the wild strain YL001. HPLC-MS analysis shown that the major antimicrobial compounds (XCN1) in ΔcpxR increased 3.84 fold compared with YL001.