| The genetic diversity of 82 lactic acid bacteria strains isolated from naturally fermented yak yogurt the samples collected from West Sichuan Plateau and 11 reference strains was studied by using 16S rDNA-PCR-RFLP and ISR-PCR-RFLP techniques, and 16S rDNA gene sequence analysis of the representative strains was done according to the. cluster by 16S rDNA-PCR-RFLP pattern. This test had also screened six lactobacilli strains by sensory evaluation and determination of acidity from the 82 LAB strains,the fermentation characteristics of the six strains,including the growth curve, acid production, viscidity of yoghurt, acetaldehyde synthesizing were studied,and 16S rDNA sequence analysis was used to demonstrate the phylogenetic relationship of these stains. The results showed that:1.Restriction analysis of 16S rDNA gene amplification products showed that Mspl was the best in the 5 restriction enzymes tested because of the richest band that it can reveal the genetic diversity. Based on the cluster of digestion of 16S rDNA gene amplification products and the phylogeny of the representative strains, the tested strains could be divided into four taxa in 61%similarity level, and taxaâ… ,â…¡,â…£were the main taxa.The stains in taxa I and IV were belong to genus Lactobacillus,and the strains in taxa II belong to the genus Enterococcu. In 81%similarity level, the tested strains could be divided into 16 taxao Restriction analysis of 16S rDNA gene amplification products also showed it had 2316S rDNA genotypes of the tested strains, and the genotypes of No.1,3,7 and 15 were main genotype.The strains of three genotypes(No.1,3,and 15) were in tax I,and the strains of genotype No.7 were in taxaâ…£. The sequence analysis of 16S rDNA gene of the representative strains and the cluster in 81%similarity level showed Lactobacillus plantarun,Lactobacillus pentosus,Lactobacillus casei Group,, Lactobacillus fermentum, Enterococcus faecalis,,Enterococcus durans maybe the main species in Yak yogurt.2. The results of the phylogen based on the sequence analysis of 16S rDNA gene of the representative strains in each taxa showed that the similarity of 16S rDNA gene sequence between the representative strains and the typical strains were under 99%,that was showed that the lactic acid bacteria in yak yoghurt were special,and may have some new taxa. Based on the 16S rDNA gene sequence analysis and cluster analysis, it showed that the LAB stains isolated from Sichuan yak yoghurt had more richness in genetic diversity, and which would provide rich material to screen superior strains to produce the yoghurt.3. Restriction analysis of ISR amplification products showed that, all the strains tested had 19 ISR genotypes.Hinfl was the best in the 5 restriction enzymes tested. The ISR-PCR-RFLP analysis result also showed that, in 60%similarity level,the tested strains could be divided into four taxa, taxa I, II, IV was the main taxa, in 80% similarity level, the tested strains could be divided into 14 taxa, the No2 genetic groups was the main ISR genetic groups.It was more different between the cluster of the digestion of ISR and 16S rDNA gene,it may be the choice of enzyme caused this difference.4. Six lactobacilli strains were selected from 82 strains isolated from the natural fermented yak yoghurt samples collected from western Sichuan Plateau by sensory evaluation and determination of acidity. Considering the fermentation characteristics of these strains, including the growth curve, acid production, viscidity of yoghurt, acetaldehyde synthesizing and the 16S rDNA gene sequence analysis,strain SAUE-1 and SAUE-5 could be used to screen the strain further for the leaven in yoghurt production.Based on the sequence analysis of 16S rDNA gene,SAUE-1 maybe the Lactobacillus plantarun,SAUE-5 and SAU4-7 maybe Lactobacillus pentosu or Lactobacillus plantarun,SAUJ-2 maybe the Lactobacillus paracasei,and SAUB-2 maybe Lactobacillus fermentum.
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