Developed the Resistance to Bacteriophage CP39 by Phase Variable Expression of Encoding the CGPTase.

Bacteriophage (phage) is regarded as an antimicrobial alternative for in food production. However, the development of phage resistance to the host is a main concern for the phage application. This study characterized the phage CP39 and investigated the phage resistance of CP39 in NCTC12662. We determined that phage CP39 belonged to the family by the WGS and phylogenetic analysis. Phage CP39 was confirmed as a capsular polysaccharide (CPS)-dependent phage by primary phage typing. It was further confirmed that the phage could not be adsorbed by the acapsular mutant Δ but showed the same lytic ability in both the wild-type strain NCTC 12662 and the Δ mutant lacking motile flagella filaments. We further determined that the gene encoding CDP-glycerol:poly (glycerophosphate) glycerophosphotransferase (CGPTase) in the CPS loci was related to phage CP39 adsorption by SNP analysis and observed a rapid development of phage resistance in NCTC 12662 during the phage infection. Furthermore, we observed a high mutation frequency of (32%), which randomly occurred in nine different sites in the gene according to colony PCR sequencing. The mutation of the gene could cause the phase variable expression of non-functional protein and allow the bacteria against the phage infection by modifying the CPS. Our study confirmed the gene responsible for the CPS-phage adsorption for the first time and demonstrated the phase variable expression as a main mechanism for the bacteria to defend phage CP39. Our study provided knowledge for the evolutionary adaption of bacteria against the bacteriophage, which could add more information to understand the phage resistance mechanism before applying in the industry.