Study On The Effect Of Salt Stress On The Division Of Lactobacillus Bulgaricus

Lactobacillus bulgaricus is used in the production of various fermented dairy products worldwide.During the preparation process as a starter,as well as in the actual fermentation process,fluctuations in osmotic pressure,temperature,p H and nutrient availability will limit the bacteria.The ability of division and proliferation reduces its fermentation performance and affects the quality and flavor of dairy products.At present,Lactobacillus bulgaricus is often under salt stress in the dairy fermentation industry.The research involving the division mechanism of lactic acid bacteria under salt stress is only the analysis of the changes in metabolism-related genes and proteins,and there is little research involving the effect of the bacterial cell in response to the salt stress environment on the divisome.In this study,by researching the changes in the formation of the divisome of Lactobacillus bulgaricus under salt stress,looking for the key genes and ways to regulate the divisome and analyzing its influence on the cell division and proliferation,to increase the culture density of Lactobacillus bulgaricus under salt stress.At the same time,it also provides a theoretical basis for further research on the division mechanism of lactic acid bacteria under stress environment.Through the determination of the salt tolerance of Lactobacillus bulgaricus sp1.1(sp1.1),the critical Na Cl salt concentration of sp1.1 bacterial cell division blocked is 2%(w/v).Analyze the changes of bacterial morphology,division ring location and morphology,DNA replication and gene expression of dna A and fts Z when sp1.1 division is blocked.The results show that the critical Na Cl salt concentration stress cannot prevent the DNA replication of Lactobacillus bulgaricus,nor can it disturb the location of the divisome ring,but it can down-regulate the expression of the genes fts Z and dna A,inhibit the assembly of the division ring,thereby making the mycelium filamentous,increasing the cell length,and accumulating chromosomes and division rings,which in turn causes the cell division to be blocked.The sp1.1 of mid-log phase cultured under the critical Na Cl salt concentration were used as the experimental group,and the corresponding period cells under normal culture conditions were used as the control group for transcriptomics sequencing.The results showed that Lactobacillus bulgaricus under Na Cl salt stress used a variety of strategies to cross-act on the divisome to regulate the division of bacterial cells,thereby adapting the bacterial growth to salt stress environment.These strategies include one-component systems serine/threonine kinase(LDB?RS01240 down-regulated);ABC transporter(Opu A up-regulated);DNA and protein damage repair(down-regulation of Dna A,upregulation of Rec A,Lex A and Spx A);protein degradation(Clp P down-regulated);chaperone protein expression(down-regulation of Dna J/K and Gro EL)and crossprotection of related proteins.Through the analysis of transcriptomics,the Na Cl salt stress response network of sp1.1 acting on the divisome were summarized.The key gene selected to act on the divisome is LDB?RS01240,the key approach is the one-component system serine/threonine kinase,and its effect on the divisome is verified.The results show that under Na Cl salt stress,Ser/Thr kinase overexpression of Lactobacillus bulgaricus reduces the accumulation of DNA in the bacterial cells and accelerates the separation of chromosomes,thereby shortening the length and cell cycle of the bacteria,reducing the accumulation of division rings,and promoting the assembly of the division ring to enhance the cell's ability to divide and proliferate.