Investigation Of The Resources Of Lactic Acid Bacteria Isolated From Natural Fermentation Yogurt In The Western Sichuan Plateau

In this study, 109 strains were isolated from the natural fermented yogurt of 28 samples in the Western Sichuan Plateau, 59 strains were bacilli and 50 strains were cocci. The assay technique of numerical taxonomy were used to study the isolates and the 12 representative strains. Base on the results of numerical taxonomy, and the phenotypic properties, the genus and species were identified.Under the pressure of the extreme environmental condition of high altitude, low temperature, drying, high radiation and large temperature difference in day and night, the isolates developed some special morphological and physiological characteristics. The diamer of cocci and the length of rods were unusually larger than of the normal lactic acid bacteria. The arrangement of some strains was long trichome. The isolated showed a wide range of growth temperature which was 18-45℃.Selection of low temperature growing strains for fermentation has advantage of reducing energy consumption.According to the results of numerical taxonomy, all the coccus strains formed one cluster at the similarity level of 72%.At the 82.8% similarity level which can distinguish all the representative species, the strains were divided into 5 clusters. Most of the strains(76%) were clustered in group 1, which indicated the low diversity of coccus. According to bacillar LAB's numerical taxonomy, all the strains tested were divided intol3 phenotypic groups at 80% similarity level which can distinguish all the representative species, the strains from the same sample were dispersed in different groups. The results showed the high phenotypic diversity of bacillus. The two dendrograms showed the common ground that most of the isolates were clustered in the different groups, with the representative species, which demonstrated that the isolates had some different phenotypic features with the representative species. The coccus strains showed higher sensitivity to streptomycin than that of the rod-shaped strains. Their sensitivity to penicillin was not significantly different with each other.Through the physiological and biochemical characteristics tests, all the bacilli strains belong to Lactobacillus including the following species, L. brevis, L. viridescens, L. lactis, L. lactis, L. hilgardii, L. leichmannii, L. fructivorans, L. bifermentans, L. delbrueckii subsp.Bulgaricus, L. casei subsp. Pseudoplantarum, L. casei subsp. casei, L. fermentum, L. acidophilus, L. curvatus.Among 50 cocci strains, they were identified to be the 4 genus of Lactococcus > Leuconostoc> Streptococcus and Enterococcus. Lactococcus include the following species, L. lactis subsp. Lactis, L. lactis. Leuconostoc includ the following species, Leu. mesenteroides, Leu. lactis, L. paramesenteroides. Streptococcus include Strep. Thermophilus. Enterococcus include the following species, E. faecalis, E. faecium and E. hirae. The strains in Enterococcus were dominance strains. The strain 3-14 could produce polyglucosan in MRS culture medium contains 10% sucrose, during 3~4 days in 20°C~25°C.