Abstract
In this study, a high-throughput sequencing technique was used to analyze bacterial and fungal diversity of two traditional Tibetan kefir grains from Linzhi (K1) and Naqu (K2) regions. Comparative bioinformatic analyses indicated that Lactobacillus kefiranofaciens, L. kefiri and Kluyveromyces marxianus were the main dominant strains in K1 and K2. In order to research the relationship of the growth of kefir grains, the biofilm and the extracellular polysaccharides (EPS) produced by microorganisms, the proliferation rate of kefir grains, the yield and chemical structure of EPS and the optimal days for biofilm formation were determined. The results showed that the growth rate, the yield of EPS and the biofilm formation ability of K1 were higher than K2, and the optimal day of their biofilm formation was the same in 10th day. Additionally, the live cells, dead cells and EPS in biofilm formation of K1 and K2 were observed by fluorescence microscope to clarify the formation process of kefir grains. To determine the influence of microbial interactions on biofilm and the formation of kefir grains, the essential role of microbial quorum sensing needs further attention.
Highlights
Kefir is an acidic, viscous, somewhat effervescent and slightly alcoholic traditional dairy beverage which is obtained by the fermentation of milk with kefir grains [1,2,3]
When the c-extracellular polysaccharide (EPS) was extracted by different methods, the bond type was destroyed and the structure of a few EPS released to the medium was consistent with the released polysaccharides (r-EPS) produced by lactic acid bacteria (LAB) [18]
The microorganism of kefir and the EPS produced by LAB associated with the grains could be considered as a biofilm [19]
Summary
Viscous, somewhat effervescent and slightly alcoholic traditional dairy beverage which is obtained by the fermentation of milk with kefir grains [1,2,3]. Many researchers have evaluated kefir grains with different microbial diversity from different countries including Argentine [7], Brazilian [8], Irish [9], Turkish [5] and Tibetan grains [10]. A composition of yeasts (Kluyveromyces, Saccharomyces and nonpathogenic strains of Candida) and some AAB were revealed in different kefir grains [11]. The total number of microorganisms isolated from various kefirs is estimated at over 300 species emphasized their complex and diverse composition [7,12]. In distinct regions of the country, the microbial diversity of kefir grains was still different. Different microbial communities of kefir grains are likely to establish in Linzhi and Naqu due to the different climate and environment
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