Outer Membrane Channel Protein TolC Regulates Escherichia coli K12 Sensitivity to Plantaricin BM-1 via the CpxR/CpxA Two-Component Regulatory System.

Plantaricin BM-1, a class IIa bacteriocin produced by Lactobacillus plantarum BM-1, has significant antibacterial activity against Gram-positive and Gram-negative bacteria. This study aimed to explore the role of the Escherichia coli K12 outer membrane (OM) channel protein TolC in the response to plantaricin BM-1. The tolC null mutant (E. coli K12∆tolC) was constructed by Red homologous recombination. The mechanism of tolC regulating the sensitivity of E. coli K12 under plantaricin BM-1 was investigated. tolC null mutation significantly increased the E. coli K12 sensitivity to plantaricin BM-1 and inhibited biofilm formation, and cells ruptured and shrunk. Proteomic analysis showed that the AcrAB-TolC and EmrAB-TolC efflux pumps were significantly (p < 0.05) upregulated in E. coli K12∆tolC. Based on the results of real-time PCR, we concluded that under plantaricin BM-1, the CpxR/CpxA two-component regulatory system of E. coli K12 responded with envelope damage, followed by activation of the transcription of marA and expression of AcrAB-TolC efflux pump. Moreover, tolC null mutation weakened the AcrAB-TolC efflux pump and then increased the sensitivity of E. coli K12 to plantaricin BM-1. These will contribute exploring the action mechanism of class IIa bacteriocins against Gram-negative bacteria.