| Lactic acid has a wide range of applications in food,medicine,cosmetics,agriculture,and chemical industries.It is an important intermediate in the metabolism of organisms and one of the three major organic acids recognized in the world.However,there are few Bacillus species that are currently reported to produce lactic acid.In this paper,a strain of DU-106 was isolated from traditional fermented yoghurt in Inner Mongolia,which has the characteristics of high yield of lactic acid.In this paper,the systematic classification status of this strain was further identified and comparative genomics analysis was carried out.The results and conclusions of this paper are as follows:The strain DU-106 is a Gram-positive bacterium,which has a rod shape,and the proliferation mode is endospore.It is a facultative anaerobic type and can produce lactic acid efficiently.The yield of L-lactic acid reaches 13.04 g/L after 72 hours of fermentation.Phylogenetic analysis based on the 16 S r RNA gene sequence revealed that the strain DU-106 belongs to the Bacillus cereus flora.By sequencing and plotting the genome of strain DU-106,the results showed that it had a circular chromosome and three plasmids,with a total genome size of 5,758,208 bp and a G + C content of 35.10%.Analysis of core genomic single nucleotide polymorphisms and comparison with known Bacillus cereus species,except for Bacillus cereus ATCC 14579 T and Bacillus thuringiensis ATCC 10792 T,strain DU-106 and other Bacillus cereus' s average nucleotide homogeneity value of the strains was less than 92%.DNA-DNA hybridization analysis showed that the DNA-DNA hybridization values of strain DU-106 and the reference strains Bacillus cereus ATCC 14579 T and Bacillus thuringiensis ATCC 10792 T were 35.40% and 14.43% respectively,indicating that DU-106 does not belong to the present known species of Bacillus cereus.Compared to Bacillus cereus ATCC 14579 T and Bacillus thuringiensis ATCC 10792 T,strain DU-106 contains higher levels of iso-C15:0 fatty acids.Comprehensive genomic analysis and DNA-DNA hybridization and physiology and biochemical characterization showed that strain DU-106 is a new strain in the Bacillus cereus flora and named Bacillus lactis.DU-106.And preserved in the Guangdong Provincial Collection of Microorganisms,deposit number: GDMCC 1.1581.The acid-tolerant,salt-tolerant and simulated gastrointestinal fluid tests showed that the strain maintained good survival in low acid,high salt and simulated gastrointestinal fluid environments,with a survival rate of 72.09% and 96.77% at p H 2.42 and 4.94,respectively.The survival rates in 0.3% bile salts,simulated gastric juice and simulated intestinal fluid were 59.67%,74.29% and 150.52%,respectively.Further comparative genomics analysis revealed that the strain was characterized by various stress-related bile salt resistance and adhesion-related genes,such as bass,cgh,cbp,fbp?,which may be caused by adhesion of host epithelial cells.And the gastrointestinal tract survives to play a probiotic role.In addition,the strain DU-106 genome lacks a virulence gene encoding cerebroside synthase,enterotoxin FM,and cytotoxin K,which was not found to be acutely toxic by an acute oral toxicity test in animals.Combining the phenotypic characteristics,genomic characteristics and probiotic characteristics of this strain can provide sufficient theoretical basis for the development of this strain DU-106 into probiotics. |
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