Biological characterization of Rhs effectors of type VI secretion system of Salmonella typhimurium

Abstract:

[Background] The type VI secretion system of bacteria acts as a weapon to kill eukaryotic predators or prokaryotic competitors by releasing toxins, known as effectors. Although some effectors have been identified, the functions of most effectors remain unknown. [Objective] To study the role of the effector Rhs encoded by rhs gene in Salmonella typhimurium. [Methods] The rhs-deleted mutants of Salmonella typhimuriumCVCC541 were constructed via Red recombination, including single gene deletion strains CVCC541Δrhs1 and CVCC541Δrhs2 and the double genes deletion strain CVCC541Δrhs1-2. Meanwhile, the corresponding gene complemented strains C-Δrhs1, C-Δrhs2 and C-Δrhs1-2 were constructed. The biochemical characteristics, biofilm formation, antibiotic resistance, competition between bacteria, bactericidal ability of complement in antiserum, dynamic distribution in vivo and the amounts of IL-18 and IL-1β released by host after infection were compared among the wild-type strain, gene-deleted strains and gene-complemented strains. [Results] Rhs did not affect the metabolism, biofilm formation, antibiotic resistance or complement bactericidal ability of Salmonella typhimurium. The competition index (CI) of CVCC541Δrhs1, CVCC541Δrhs2 and CVCC541Δrhs1-2 was 0.85, 0.77 and 0.87, respectively, which indicated slightly weakened virulence. Compared with the wild-type strain, CVCC541Δrhs1, CVCC541Δrhs2 and CVCC541Δrhs1-2 showed decreased number in the liver and spleen of mice (P<0.05). The host secretion of IL-1β and IL-18 was correlated with the Rhs of Salmonella typhimurium(P<0.05). [Conclusion] The Rhs effectors of Salmonella typhimuriumplay a role in the competition between bacteria, the colonization of bacteria in host organs, and the regulation of the secretion of inflammatory cytokines IL-1β and IL-18 in the host.