16S ribosomal DNA analysis and characterization of lactic acid bacteria associated with traditional Tibetan Qula cheese made from yak milk

Abstract

Twenty strains of lactic acid bacteria were isolated from six traditional Tibetan Qula cheese made from yak which were collected from northwest China, including Tibet, Qinghai and Gansu province. These isolates were subjected to phenotypic and genetic analyses. All isolates were Gram-positive and catalase-negative cocci that produced gas from glucose and formed D(-) isomer of lactate. Most isolates were able to grow in de Man, Rogosa and Sharpe (MRS) broth at pH values 3.0-9.0 and in 6.5% NaCl (w/v). According to analytical profile index 50 carbohydrates (API 50 CH) fermentation patterns of amygdalin and arabinose, these isolates were divided into three groups (A to C). On the basis of the phylogenetic trees of 16S ribosomal DNA (rDNA) sequence, the strains in all groups were placed in the cluster making up the genus Leuconostoc, which showed that all strains should belong to Leuconostoc species. Strains in Group A and Group B exhibited similarity of 16S rDNA sequence of over 99% to Leuconostoc mesenteroides, indicating that they each comprised a single species. Strains in group C were assigned to the Leuconostoc pseudomesenteroides and their 16S rDNA sequence showed a similarity of over 99%. This study demonstrated that Leuconostoc was the dominant member among lactic acid bacteria in Qula cheese.