Gene deletion and phenotype observation of two-component system VgrS-VgrR in Xanthomonas axonopodis pv. manihotis

Abstract:

[Objective] In this study, we investigated the relationship between the VgrS-VgrR two-component system (TCS) of Xanthomonas axonopodis pv. manihotis (Xam) and the bacterial pathogenicity. The study can provide molecular biological evidence for the effective prevention and control of cassava bacterial blight. [Methods] We constructed the insertion-inactivation mutants of vgrS and vgrR by homologous recombination, and constructed the complementary strains of each mutant by using the mobile cosmid vector pHM1. The study measured the pathogenicity of each mutant, its swimming and the changing in extracellular enzyme and extracellular polysaccharide production. We also observed the bacterial response to hydrogen peroxide and metal ion stress. [Results] Compared with wild-type strain, both vgrS and vgrR mutants exhibited significantly reduced pathogenicity after inoculation of the host plant cassava. Both mutants exhibited decreased swimming, reduced protease activity and hydrogen peroxide tolerance. Under the stress conditions of high concentrations of metal ions Fe²⁺, Fe³⁺, Cu²⁺, Ni²⁺, Zn²⁺ and Cu²⁺, the mutants' growth were also significantly decreased. However, the extracellular polysaccharide content of vgrS and vgrR mutants increased dramatically, which was 2.14 and 1.89 times that of the wild type, respectively. [Conclusion] The results clarified the important role of the VgrS-VgrR TCS in the pathogenesis of Xam, and provided clues for further research on the regulation mechanism of VgrS-VgrR and drug screening targeting Xam.

Key words:Xanthomonas axonopodis pv. manihotis (Xam);two-component system;mutants;phenotype screening