A survey of the bacterial composition of kurut from Tibet using a culture-independent approach.

Kurut (fermented yak milk) made by natural fermentation is a very important dairy food for the local people in Tibet (China). It is important to fully understand the bacterial composition of kurut for quality improvement and industrial production. Because more than 99% of prokaryotes cannot be cultured and identified by methods currently used in taxonomy, we applied a culture-independent approach to explore the microbial biodiversity of this traditional food. In this study, a bacterial 16S rRNA gene clone library, including 460 clones, was constructed using total DNA extracted from 30 samples of kurut. After screening by restriction fragment length polymorphism (RFLP) analysis, 56 operational taxonomic units (OTU) with unique RFLP patterns were obtained. Then, 1 representative sequence of every OTU was sequenced and phylogenetically analyzed. The representative phylotypes were affiliated with 5 groups, including Lactococcus lactis ssp. lactis, Lactobacillus helveticus, Streptococcus thermophilus, Lactobacillus delbrueckii ssp. bulgaricus, and Acetobacter. In addition, nearly one-third of the representative clones (132 clones) had low similarity to species in GenBank (<97%), and these phylotypes were regarded as unknown bacteria. The characteristics of kurut are determined not only by lactic acid bacteria well known by the culture-dependent approach but also by bacteria that have not yet been identified.

Mongoliitalea lutea gen. nov., sp. nov., an alkaliphilic, halotolerant bacterium isolated from a haloalkaline lake.

Two bacterial isolates from the surface water of a haloalkaline lake on the Mongolia Plateau, strains MIM18(T) and MIM19, were characterized; their morphological, physiological and chemotaxonomic characters, and phylogenetic position based on 16S rRNA gene sequences, were determined. The two strains were alkaliphilic, halotolerant, non-motile, aerobic, Gram-negative, orange-red, rod-shaped and oxidase-positive. Growth was observed in 0-5.5% (w/v) NaCl, with optimum growth at 1%. The temperature range for growth was 0-41 °C, with good growth at 28-37 °C and optimum growth at 30-33 °C. The DNA G+C content was 39.8-41.2 mol%. The strains contained menaquinone MK-7 as the major respiratory quinone and phosphatidylcholine, phosphatidylglycerol and phosphatidylethanolamine as the major polar lipids. Predominant cellular fatty acids were iso-C(15:0) (28.1-29.3%), iso-C(17:0) 3-OH (14.6-18.8%), C(15:1)ω6c (5.3-8.6%), C(14:0) 2-OH and/or iso-C(15:0) 2-OH (5.4-6.1%), and iso-C(17:1)ω9c and/or C(16:0) 10-methyl (5.0-6.8%). 16S rRNA gene sequence analysis showed that Belliella and Nitritalea of the family Cyclobacteriaceae were the closest related species with sequence similarities of 91.7-92.3% and 88.2%, respectively, with strains of these genera; other members of the Cyclobacteriaceae had sequence similarities lower than 88%. Phylogenetic analysis indicated that the strains formed a deep-rooted lineage distinct from the clades represented by the genera Belliella, Nitritalea, Indibacter, Aquiflexum, Echinicola, Litoribacter, Cyclobacterium and Algoriphagus. Based on the phenotypic and phylogenetic characteristics mentioned above, the two strains are representatives of a single novel species in a new genus; the name Mongoliitalea lutea gen. nov., sp. nov. is proposed, with MIM18(T) (=ACCC 05421(T)=KCTC 23224(T)) as the type strain.

Diversity of lactic acid bacteria associated with traditional fermented dairy products in Mongolia.

Spontaneous milk fermentation has a long history in Mongolia, and beneficial microorganisms have been handed down from one generation to the next for use in fermented dairy products. The objective of this study was to investigate the diversity of lactic acid bacteria (LAB) communities in fermented yak, mare, goat, and cow milk products by analyzing 189 samples collected from 13 different regions in Mongolia. The LAB counts in these samples varied from 3.41 to 9.03 log cfu/mL. Fermented yak and mare milks had almost identical mean numbers of LAB, which were significantly higher than those in fermented goat milk but slightly lower than those in fermented cow milk. In total, 668 isolates were obtained from these samples using de Man, Rogosa, and Sharpe agar and M17 agar. Each isolate was considered to be presumptive LAB based on gram-positive and catalase-negative properties, and was identified at the species level by 16S rRNA gene sequencing, multiplex PCR assay, and restriction fragment length polymorphism analysis. All isolates from Mongolian dairy products were accurately identified as Enterococcus faecalis (1 strain), Enterococcus durans (3 strains), Lactobacillus brevis (3 strains), Lactobacillus buchneri (2 strains), Lactobacillus casei (16 strains), Lactobacillus delbrueckii ssp. bulgaricus (142 strains), Lactobacillus diolivorans (17 strains), Lactobacillus fermentum (42 strains), Lactobacillus helveticus (183 strains), Lactobacillus kefiri (6 strains), Lactobacillus plantarum ssp. plantarum (7 strains), Lactococcus lactis ssp. lactis (7 strains), Leuconostoc lactis (22 strains), Leuconostoc mesenteroides (21 strains), Streptococcus thermophilus (195 strains), and Weissella cibaria (1 strain). The predominant LAB were Strep. thermophilus and Lb. helveticus, which were isolated from all sampling sites. The results demonstrate that traditional fermented dairy products from different regions of Mongolia have complex compositions of LAB species. Such diversity of LAB provides useful information for further studies of probiotic strain selection and starter culture design, with regard to the industrial production of traditional fermented milk.