Mechanisms Of Milk Fat Globule Membrane Protection Against Acid Stress In Lactobacillus Acidophilus CICC 6074

Lactobacillus acidophilus is an important member of lactic acid bacteria,which has important functions of regulating the intestinal immune system and enhancing the body’s immunity.However,in order to perform the functions of these probiotics,it is first necessary to improve the resistance of lactic acid bacteria to gastrointestinal acid stress.Studies have shown that milk fat globule membrane can play a better probiotic function by synergizing with probiotics.We suspect that the milk fat globule membrane protein on its surface improves the acid stress resistance of lactic acid bacteria.The mechanism is still poorly understood.In this paper,L.acidophilus CICC 6074 is the research object to explore its own acid resistance mechanism and the protective mechanism of milk fat globular membrane protein under acid stress.The main research contents of this topic are as follows:1.By comparing the survival ability of L.acidophilus CICC 6074 at different pH,pH=2.5 was selected as the acid stress condition for subsequent experiments.Proteomics analysis of the protein changes of strains before and after acid stress revealed that 264 proteins had significant changes,of which 119 were up-regulated proteins and 145 were down-regulated proteins.Then,these proteins were enriched and analyzed through databases such as GO,COG,KEGG,and the results showed that three metabolic pathways were significantly affected before and after the acid stress of the strain:purine metabolism,phosphotransferase system,and sphingolipid metabolism.In addition,these proteins are also involved in processes such as amino acid metabolism,ribosomal synthesis protein,ABC transporter,and DNA and protein repair.The results showed that under strong acid conditions,L.acidophilus could resist acid stress by down-regulating related proteins such as DNA replication,translation,and transport to reduce protein synthesis and energy consumption.At the same time,it up-regulates amino acid metabolism and DNA repair and other related proteins to reduce and repair the damage caused by acid stress to the strain.2.The role of milk fat globule membrane protein in protecting L.acidophilus against acid stress was studied.Exogenous addition of globular membrane protein can significantly improve the growth performance of L.acidophilus and the survival rate under acid stress conditions.After the strain is treated with pH 2.5 stress for 3 hours,the cell survival rate is 1.9 times that of no addition.At the same time,analysis of the physiological characteristics of cells found that the strains added with milk fat globular membrane protein maintained higher pHi,H~+-ATPase activity and amino acid content,which could effectively regulate the stability of intracellular pH and enhance the acid stress resistance of the bacteria.Finally,scanning electron microscopy found that the addition of milk fat globular membrane protein could better maintain the integrity of the bacterial structure,reduce the outflow of intracellular substances and the entry of extracellular harmful substances,thereby effectively reducing the damage to cells caused by acid stress.3.The changes of L.acidophilus acid stress resistance before and after the protection of milk fat globule membrane proteins were analyzed by proteomics.After adding milk fat globule membrane protein,a total of 538 proteins with significant changes were identified,including 439 up-regulated proteins and 99 down-regulated proteins.The enrichment analysis of these proteins by GO,COG,and KEGG found that differential protein functions are mainly divided into three categories:cell metabolism;DNA synthesis,transcription and translation;DNA and protein repair.The addition of milk fat globular membrane protein will also change the expression of regulatory proteins for cell material metabolism and energy production,making it have higher ATPase activity,peptidoglycan synthesis and amino acid metabolism activity,which is beneficial to reduce the damage to cells caused by acid stress.In the pathways related to DNA synthesis,transcription and translation,the addition of milk fat globular membrane protein could promote the expression of proteins related to DNA replication,transcription and translation,and maintain the normal metabolism of bacteria under acid stress.Finally,in terms of DNA and protein repair,the addition of milk fat globule membrane protein can promote the production of a large number of DNA repair proteins,but there are fewer molecular chaperone proteins,thereby repairing DNA and protein damage caused by acid stress.In summary,we have explored the acid resistance mechanism of L.acidophilus CICC 6074 and have a preliminary understanding.Exogenous addition of milk fat globular membrane protein can improve the acid stress resistance of L.acidophilus CICC 6074,and has a preliminary understanding of its mechanism of action,which provides a new idea for improving the acid stress resistance of lactic acid bacteria.In summary,we explored the possible acid-resistance mechanism of Lactobacillus acidophilus CICC 6074.Exogenous addition of milk fat bulbous membrane protein can improve the acid stress resistance of Lactobacillus acidophilus CICC 6074,and preliminary discussion was made on the mechanism of action,providing a new idea for improving the acid stress resistance of Lactobacillus.