Diversity and functions of lactic acid bacteria in traditional handmade dairy products in Tashkurgan region

Abstract:

[Background] Traditional handmade dairy products are the favorite food in Tajik agricultural and pastoral areas. They contain abundant lactic acid bacterial resources which need to be exploited and utilized. [Objective] By analyzing the diversity and functions of lactic acid bacteria in traditional homemade dairy products from Tajik agricultural and pastoral areas, we aim to aid in the exploration and protection of microbial resources and provide a theoretical basis for evaluating the safety of traditional dairy products. [Methods] The V3–V4 variable region of bacterial 16S rRNA gene was subjected to high-throughput sequencing. The culturable suspected lactic acid bacteria were screened by the conventional culture methods in the MRS, Lee’s, and M17 media and identified by physiological and biochemical tests and 16S rRNA gene sequence homology. Furthermore, the microbial species and gene function information in the dairy products in Tajik autonomous county of Taxkorgan were analyzed. [Results] There were 37 bacterial genera and 65 bacterial species in the 4 dairy samples, among which Lactobacillus and Streptococcus were the dominant bacterial genera in cheese and yogurt, and Lactobacillus helveticus was the dominant species. A small amount of pathogenic bacteria existed in the cheese samples. Moreover, 38 culturable suspected lactic acid bacterial strains were identified from MRS, M17, and Lee’s media, including 3 strains of Bacillus subtilis, 1 strain of B. luti, 1 strain of B. paranthracis, 9 strains of Lactobacillus paracasei, 3 strains of Enterococcus hormeachei, 1 strain of Staphylococcus heamolyticus, 1 strain of Klebsiella pneumoniae, 10 strains of Leuconostoc pseudomesenteroides, 2 strains of Leuconostoc mesenteroides, 4 strains of Lactobacillus plantarum, 1 strain of Acetobacter senegalensis, 1 strain of Enterococcus durans, and 1 strain of Enterobacter faecalis. Among them, the dominant genus was Leuconostoc, followed by Lactobacillus. The 38 strains were classified into 7 genera and 13 species. The results indicated that the conventional culture method can accurately identify lactic acid bacteria to the species level. Representative 11 strains of lactic acid bacteria were selected from 38 strains for antibacterial tests, and all 11 the strains had inhibitory effects on Escherichia coli and B. subtilis. The COG (clusters of orthologous groups of proteins) function prediction showed that the microorganisms in cheese carried rich genes involved in amino acid transport and metabolism. Although there were significant differences in the bacterial community composition between samples, their functions were highly similar. [Conclusion] The diversity of lactic acid bacteria in four traditional handmade dairy products in Tajik autonomous county of Taxkorgan, Xinjiang was studied by combining the molecular biological methods and the conventional culture method. The richness and diversity of lactic acid bacteria in the dairy products were low, and there were some pathogenic bacteria. The combination of the two methods in this study comprehensively revealed the microbial composition in the dairy products. The findings provided basic data for the industrial production and protection of the abundant microbial resources in this area and laid a foundation for evaluating the safety of lactic acid bacteria in traditional dairy products.