Oxygen-tolerant Domestication And Its Potential Molecular Mechanism Of Bifidobacterium Animalis Subsp. Lactis M8

Oxygen has the toxic effect on Bifidobacterium,which leads to the damage of its viability,and limitation of production and application.In order to improve the oxygen tolerance of Bfidobacteria,the method of changing the partial pressure of oxygen in liquid medium was used to domesticate the oxygen tolerance of Bifidobacterium animalis subsp.lactis M8.The effect of oxygen on Bifidobacterium animalis subsp.lactis M8 was evaluated by physiological characteristics,oxygen-tolerance related NADH oxidase activity,and change in cell membrane fluidity.In order to further explore the reasons for the oxygen tolerance of Bifidobacterium animalis subsp.lactis M8 after oxygen-tolerant domestication,the RNA-seq method was carried out to establish the differential gene map of original and the oxygen-tolerant domestication of Bifidobacterium animalis subsp.lactis M8 at 30 and 60 min under 9%oxygen environment.The conclusions were as follows:Compared with the original strain,oxygen-tolerant domestication 1000 generations of strain was cultured in aerobic and anaerobic environment for 24 hours,the pH of culture medium significantly decreased by 0.23 and 0.27(P<0.05),and acid production capacity significantly increased.The relative bacterial growth ratio(RBGR)and NADH oxidase activity significantly increased by 0.47 and 31.14 U(P<0.05),and the oxygen-tolerance was significantly enhanced.The content of unsaturated fatty acid increased significantly by 17.26%(P<0.05),and the cell membrane fluidity was enhanced.Compared with the original strain,at 30 min of oxygen stress,a total of 210 differentially expressed genes with significantly changes were obtained in the oxygen-tolerant domesticated Bifidobacterium animalis subsp.lactis M8,of which 59 genes were up-regulated and 151 genes were down-regulated(P<0.05).At 60 min of oxygen stress,a total of 217 differentially expressed genes with significantly changes were obtained,of which 80 genes were up-regulated and 137 genes were down-regulated(P<0.05).Using KEGG,GO and other databases to analyze the function and involved metabolic pathways of differentially expressed genes,the mechanism of oxygen-tolerance was then proposed,including:?Removal of active oxides,the expression of NADH oxidase was increased.?Regulating carbohydrate metabolism,involved in the lactose,starch and sucrose metabolism gene,which increased lactose utilization and decrease starch and sucrose utilization.?Regulating metabolism and composition of fatty acid,the related genes involved in fatty acid anabolism,content and composition of unsaturated fatty acids and their expression in the proportion of total fatty acids were up-regulated,and the cells initiated their temporary adaptive mechanisms,self-regulated the cells and enhanced their adaptability.?Anti-stress response,genes of branched-chain amino acids transport pathway expression were significantly up-regulated,which provided raw materials for protein synthesis,and generated the energy for oxidative stress response.