Abstract: Objective · To investigate the correlation between methylation and the activity of transcriptional regulator PhoP in Salmonella enterica serovar Typhimurium (S. Typhimurium), and screen for the methyltransferase of PhoP. Methods · The methylation level of PhoP in S. Typhimurium under different culture conditions was determinedWestern blotting. The transcription levels of phoP and the genes regulatedphoP were examined to screen for the methyltransferase of PhoP after overexpressing methyltransferase candidates predictedbioinformatics. And then methyltransferase assay was verified in vitro. The transcription levels of phoP and its methyltransferase were determinedreal-time PCR in high concentration of Mg2+ or weak acid conditions. Results · As the concentration of Mg2+increased in the medium, the methylation level of PhoP increased, and its methylation level decreased after S. Typhimurium was stimulatedweak acid. In the screening of 9 methyltransferases predictedbioinformatics, over of STM14_0023 reduced the transcription level of phoP and its downstream genes and the protein level of PhoP in vivo, but knockout of STM14_0023 had no effect on the of phoP and its downstream genes. STM14_0023 was capable of methylating PhoP in vitro and could also increase the methylation level of PhoP after over of STM14_0023 in vivo. Under the condition of high concentration of Mg2+ when the of phoP was inhibited, the transcriptional level of STM14_0023 was reduced. Conclusion · STM14_0023 is the methyltransferase of PhoP, and methylation inhibits PhoP activity.

Key words: Salmonella enterica serovar Typhimurium, PhoP, methylation, STM14_0023, virulence