Acidphilic Characteristics And Mechanism Of Lactobacillus Paracei L105 Induced By Space Flight

The starting strain of this paper is Lactobacillus casei L105,which has been proved by laboratory research that L105 has good fermentation performance.In this paper,Lactobacillus parmesis L105 freeze-dried bacteria powder was placed in the aseptic canaliculus and carried in the "Shenzhou eleven" return spacecraft to induce the strain to be mutagenic in space.The mutagenic strain was cultured and diluted with 10 times dilution method.The strain was coated on the solid medium.After 48 h,the single colony on the plate was selected and picked.The strain was picked up by DNA,PCR was amplified,and the strain was identified.Genetic stability was evaluated,and other properties of mutant strains were measured,including morphological identification,growth curve,acid tolerance and bile salt tolerance evaluation,determination of extracellular polysaccharide yield,hydrophobicity and so on.The mechanism of increasing acid production was also discussed.Through the above experiments,the following results are obtained.(1)Eighty-two strains of Lactobacillus casei were obtained by isolation and identification.By screening the acid content of the fermented milk by titrating acidity,1 mutant strains producing acid higher than the starting strain were screened,and the acid production and genetic stability were evaluated.Finally,1 strains of Lactobacillus Parmesan A-4-2 with high acid yield were obtained.The acidity of this strain after continuous fermentation for 7d was 229.16 degree T,compared with the starting strain L105(213.06 T)increased by 16.1 T.(2)The other properties of the mutant strains evaluation: the mutant strain obtained by screening the determination of morphological observation,growth curve,acid,bile salt tolerance,extracellular polysaccharide content as well as the determination of surface hydrophobicity,the results showed that gram staining,electron micr oscopy and transmission electron microscope,compared to departure strains mutant strain has no apparent change in morphology;Through statistical analysis of A-4-2 mutant strain under aerobic conditions the growth of basic consistent with the wild strains,and acid,bile salt resistant ability did not change,also shows that the acid can improve the production at the same time,does not lose its original growth characteristics.(3)To explore the causes of the increase of acid production through the determination of whole-genome resequencing and the determination of the activity and gene expression of beta-galactosidase.The results showed that the activity of beta-galactosidase and the gene expression were significantly higher than that of the original strain,and it was proved that the activity of beta-galactosidase was closely related to the production of acid.One strains of Lactobacillus pareus A-4-2 with high acid and stable heredity were screened by space mutation test,and the reason for the increase of acid production was explored,which laid the foundation for the extensive application of Lactobacillus Parea.