Influences On Mice Intestinal Microenvironment By Bacteriocin-producing Lactic Acid Bacteria

Gut microbiota plays an important role in determining the health of the host.Abnormal changes in the intestinal microenvironment may lead to the occurrence of multiple host diseases.Some lactic acid bacteria have been proved to improve intestinal environment and promote host health by regulating intestinal flora.Except for the extensive study of organic acids produced by lactic acid bacteria,bacteriocins produced by lactic acid bacteria have rarely been involved in studies about their affects on the intestinal microenvironment and health of the host.Bacteriocin production ability is one of the important characteristics of lactic acid bacteria,with great significance when it exerts the antagonistic effect against pathogenic bacteria.However,with the increasing use of lactic acid bacteria in people's daily lives,whether bacteriocins produced by lactic acid bacteria could affect the intestinal microenvironment of healthy hosts has become an urgent problem to be solved.The purpose of this study is to analyze the effects of lactic acid bacteria producing and non-producing bacteriocins on intestinal microenvironment and mouse health in normal mice,and explain the potential effects of bacteriocins produced by lactic acid bacteria on normal hosts,and to provide theoretical support for functional lactic acid bacteria development.The main findings are listed as follows:In this study,Lactobacillus acidophilus CCFM 720,the bacteriocin mutant strain abtained from L.acidophilus JCM 1132 by multiple passages,and the starting strain as a strict pair of strains producing and non-producing bacteriocins.Using the Oxford cup method in conjunction with the elimination of organic acids and hydrogen peroxide,protease sensitivity assays,and tests of growth curves,generation times,and resistance to acid and bile salts,5 additional pairs of bacteriocin producing and non-producing lactic acid bacteria from different species were determinded.Further,the effects of bacteriocin produced by lactic acid bacteria on the intestinal microbiota,metabolites,and related immune and biochemical parameters of normal host were studied by treatment of different lactic acid bacteria on normal mice.Firstly,the changes in the water and food intake of mice after gavage showed that although there was no absolute correlation between changes in water or food intake and bacteriocin-producing or not,the bacteriocin-producing lactic acid bacteria(L.acidophilus JCM 1132 and L.acidophilus CCFM 720)could affect the amount of water and food intake in mice.However,these differents did not affect the body weight gain in mice.Secondly,through the analysis of the influence on gut microbiota,it was found that most lactic acid bacteria had no effect on the alpha diversity of the intestinal flora in normal mice,and only a few individual lactic acid bacteria caused variety in alpha diversity which cannot be attributed to the presence of bacteriocins;However,bacteriocin production by lactic acid bacteria could significantly affect the abundance of microorganisms in the intestinal tract of mice,such as Actinobacteria and Verrucomicrobia.This effect may result from the feedback effects of antagonism against some microflora in the gut by lactic acid bacteria bacteriocins;Bacteriocin produced by lactic acid bacteria would also directly affect the abundance of microorganisms such as Bifidobacteroides,Akkermansia,Mucispirillum,Ruminococcus and Turicibacter in the intestine.Therefore,whether lactic acid bacteria can produce bacteriocin may be an important factor in regulating beneficial microbe such as Bifidobacteroides and Akkermansia.Thirdly,analysis of the concentration of intestinal short-chain fatty acids(SCFAs)in mice gut indicated that most lactic acid bacteria have little effect on the concentration of SCFAs in healthy intestines.However,L.acidophilus CCFM 720 and JCM 1132 showed significant differences in the effects of the 3 SCFAs contents in the intestinal tract of mice.This may be due to the differential influence of the bacteriocins produced by L.acidophilus on the intestinal microflora.So,whether lactic acid bacteria produce bacteriocins or not could also affect the abilities of the lactic acid bacteria in regulating the concentration of intestinal SCFAs.Fourthly,from the results of immunological tests on mice,it was found that although the results from the proportion of mouse Treg cells could not prove whether the bacteriocin produced by lactic acid bacteria would directly affect the host immune system,the production of bacteriocins by lactic acid bacteria would directly affect the immune system such as the levels of some cytokines(IL-6,IL-10)in mice.In addition,there were negatively correlation between propionic acid levels in the proinflammatory factors such as IL-1?,IL-6,and IL-12.Therefore,the bacteriocin produced by lactic acid bacteria may regulate the host's immune system by regulating the level of SCFAs in the host's intestine.Finally,through the analysis of blood biochemical indicators and morphology of colon tissue,it was found that bacteriocin production by lactic acid bacteria directly affected the C-reactive protein levels in mice,but did not affect the morphology of colon tissues in normal mice.Taken together,it can be concluded that the bacteriocin produced by lactic acid bacteria can affect the physiological metabolism of the host by regulating the intestinal environment(microbiota,SCFAs and immune system).