A Study On The Acid Resistance Of Lactobacillus Bulgaricus LJJ Based On The Omics Technology

Yoghurt is highly favored by the public for its high nutrition.Lactic acid bacteria play an important role in the nutrition value and healthy function,which can transform large protein molecules into smaller molecules easily absorbed by the human body.Nevertheless,it's inevitable that lactic acid bacteria may be subjected to the extreme environment in the gastric acid.Most bacterial strains have died before reaching intestinal tract with only survived ones in the acid environment(pH=2.5-3.5)can fulfil the probiotic role.Therefore,research in the acid-fast ability of Lactobacillus bulgaricus and its probiotic function have both theoretical and practical implications.The main research objects are Lactobacillus bulgaricus LJJ separated from the yoghurt on sale and model strain ATCC11842.Firstly,the strong acid-resistant strains are selected.Secondly,the basic information of the genome is obtained by the whole genome sequencing.Thirdly,the comparative genomics are adopted to find the different genes.Finally,the relevant acid resistant genes are screened out for verification.The research results are listed as follows:1.Different strains of Lactobacillus bulgaricus have different forms in morphology,growth rate,acid-producing capability and ability of acidification.The LJJ has the strongest ability(93.1% survival rate when incubation for 3 h under pH=3.0;while the survival rate is 66% under pH=2);while the type strain ATCC 11842 has the lowest acid-resistant ability(85.2% survival rate when incubation for 3 h under pH=3.0;while the survival rate is only 29.2% under pH=2).2.By the homologous and cluster analysis,different genomes have been found within Lactobacillus bulgaricus LJJ and the type strain ATCC11842.They share 1441 genes with 445 specific genes for Lactobacillus bulgaricus LJJ and 126 specific ones for the type strain;3.By KEGG pathway analysis of the specific genes,16 genes(e.g.TC.APA?argH?asnB,etc.)are found to be relevant with the acid-resistance of LJJ.Finally,dapA?LuxS?dapH and LysC are verified to be relevant with the acid resistance by PCR and statistical methods.Relevant metabolic pathways include pathway of amino acid metabolism(synthesis of lysine),two-component system and the synthesis of biological membrane.