Pyrosequencing analysis of the microbial diversity of airag, khoormog and tarag, traditional fermented dairy products of mongolia

Abstract

Here, we used pyrosequencing to obtain a detailed analysis of the microbial diversities of traditional fermented dairy products of Mongolia. From 22 Airag (fermented mare's milk), 5 Khoormog (fermented camel's milk) and 26 Tarag (fermented milk of cows, goats and yaks) samples collected in the Mongolian provinces of Arhangai, Bulgan, Dundgobi, Tov, Uburhangai and Umnugobi, we obtained a total of 81 operational taxonomic units, which were assigned to 15 families, 21 genera and 41 species in 3 phyla. The genus Lactobacillus is a core bacterial component of Mongolian fermented milks, and Lactobacillus helveticus, Lactobacillus kefiranofaciens and Lactobacillus delbrueckii were the predominant species of lactic acid bacteria (LAB) in the Airag, Khoormog and Tarag samples, respectively. By using this pyrosequencing approach, we successfully detected most LAB species that have been isolated as well as seven LAB species that have not been found in our previous culture-based study. A subsequent analysis of the principal components of the samples revealed that L. delbrueckii, L. helveticus, L. kefiranofaciens and Streptococcus thermophilus were the main factors influencing the microbial diversity of these Mongolian traditional fermented dairy products and that this diversity correlated with the animal species from which the milk was sourced.

Keywords: Airag; Khoormog; Mongolian traditional dairy products; Tarag; microbial diversity; pyroseqencing.

Fig. 1.

Phylogenetic tree based on 16S rRNA gene sequences showing the taxonomic positions of the OTUs that showed less than 97% sequence similarities with their closest related species. The tree was constructed by using the neighbor-joining method on the basis of a comparison of approximately 300 bp; Escherichia coli ATCC 11775^T served as an out-group. Bootstrap values (%) based on 1000 replicates are given at the nodes. Bar, 5% sequence divergence.

Fig. 2.

Two-dimensional scatter plot of PC1 and PC2 scores from the principal component analysis of bacterial species diversity. The sample plots were assigned on the basis of (A) the animal species from which the milk was sourced for the preparation of the fermented dairy products and (B) the geographic sampling locations. The four largest loads of bacterial species are shown with arrows. The contributions of PC1 (horizontal axis) and PC2 (vertical axis) are 76.1% and 21.1%, respectively.