Characterization of Two-Component System CitB Family in Salmonella Pullorum

Salmonella enterica, serovar Gallinarum, biovar Pullorum, is an avian-specific pathogen which has caused considerable economic losses to the poultry industry worldwide. Two-component systems (TCSs) play an essential role in obtaining nutrients, detecting the presence of neighboring bacteria and regulating the expression of virulence factors. The genome analysis of S. Pullorum strain S06004 suggesting the carriage of 22 pairs of TCSs, which belong to five families named CitB, OmpR, NarL, Chemotaxis and LuxR. In the CitB family, three pairs of TCSs, namely CitA-CitB, DcuS-DcuR and DpiB-DpiA, remain unaddressed in S. Pullorum. To systematically investigate the function of the CitB family in S. Pullorum, four mutants, Delta citAB (abbreviated as Delta cit), Delta dcuSR (Delta dcu), Delta dpiBA (Delta dpi) and Delta citAB Delta dcuSR Delta dpiBA (Delta 3), were made using the CRISPR/Cas9 system. The results demonstrated that the CitB family did not affect the growth of bacteria, the results of biochemical tests, invasion and proliferation in chicken macrophage HD-11 cells and the expression of fimbrial protein. But the mutants showed thicker biofilm formation, higher resistance to antimicrobial agents, enhanced tolerance to inhibition by egg albumen and increased virulence in chicken embryos. Moreover, the deletion of Dpi TCS was detrimental to survival after exposure to hyperosmotic and oxidative environments, as well as the long-term colonization of the small intestine of chickens. Collectively, we provided new knowledge regarding the possible role of the CitB family involved in the pathogenic processes of S. Pullorum.

Automated summary

Salmonella enterica, serovar Gallinarum biovar Pullorum is a pathogen specific to avians, causing significant economic losses in the poultry industry globally. The study analyzed the genome of S. Pullorum strain S06004 and identified 22 pairs of two-component systems (TCSs) belonging to five families. The role of the CitB family in S. Pullorum pathogenesis was investigated using mutants generated through the CRISPR/Cas9 system. It was found that the CitB family does not affect bacterial growth, biochemical properties, invasion, proliferation, or fimbrial protein expression. However, the mutants showed enhanced biofilm formation, antimicrobial resistance, inhibition tolerance, and virulence in chicken embryos. Deletion of the Dpi TCS had detrimental effects on survival in hyperosmotic and oxidative environments, as well as long-term colonization of the chicken small intestine.