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.