Identification Of BREX System In Lactobaeillus Casei Zhang And Correlation Analysis Between DNA Methylation And Biological Characteristics

Bacteriophage exclusion(BREX)system is a novel prokaryotic defense system against bacteriophages.To our knowledge,no study has systematically characterized the function of the BREX system in lactic acid bacteria.Lactobacillus(L.)casei Zhang is a koumiss-originated probiotic bacterium that confers beneficial effects to the host,and it is thus increasingly used in dairy industry.By using single-molecule real-time(SMRT)sequencing,we previously identified N6-methyladenine(m6A)signatures in the genome of L.casei Zhang and two putative methyltransferase(MTase),namely LCAZH 2056(pglX)and LCAZH 2054.This study focused on the two methyltransferase,identified an anti-phage system,and analyzed the function of two methyltransferase by using gene knockout technology and SMRT sequence technology.Meanwhile,this study explored the relation between the DNA methylation and biological characteristics.The results were as follows(1)We found an eight gene BREX system in L.casei Zhang genome.pglX controlled the N6-methyladenine DNA methylation in L.casei Zhang,furthermore the pglX is crucial in BREX function.LCAZH 2054 is not the control gene of L.casei Zhang methylation.Maybe this gene could regulate the specificity of BREX system.(2)N6-methyladenine methylation's present or not has no impact on the bacterial and colony morphology.Lacking DNA methylation can accelerates the growth of L.casei Zhang ?pglX in the logarithmic growth phase.By analysing the transcriptome,we found that vanish of DNA methylation can active the expression of genes related with carbohydrate metabolism,pyruvate metabolism and amino acid metabolism.(3)There is little impact on the anti-acid or bile ability when lacking the DNA methylation.But the anti-oxidant ability was significantly decreased in the L.casei Zhang?pglX.By analysing the transcriptome data,we found the genes coding thioredoxin,replication,recombination and repair,lipid synthesis and components of diversity pathways were regulated in L.casei Zhang ApglX.In summary,this study identified a BREX anti-phage system in the L.casei Zhang genome,and the methyltransferase pglX gene plays a significant role in this system.The methyltransferase LCAZH 2054 gene may play a role in regulating the specificity of BREX system,but still need further verification.In addition,m6A methylation has a certain role in logarithmic growth phase and the antioxidant ability.