Determination of water and kefir grain microbiotas by metagenomic analysis

The natural grains that are the subject of research in this project include water-type and milk kefir grains. The formation of different products in the field of fermented products is due to culture and raw material sources. Both kefir grains mentioned in this research are structures that are taken from the product after fermentation and reused. There is no other natural structure that produces fermented products in this way, which is sustainable and reusable. Although these natural grains contain different species and genera, they contain a very high amount of lactic acid bacteria, acetic acid bacteria, and yeasts. Therefore, the aim of this project is to determine the differences between the microbiota of these natural grain structures. In this project, three samples from each natural grain group were obtained from different regions in Turkey, regular activation was ensured, and DNA isolations were performed directly from the grains independently of culture. Using next-generation sequencing technologies and a metagenomic approach, the entire genome was determined. As a result, the species diversity was determined to be 931-17836 in the three different milk kefir grains and 299-16759 in the water kefir grains. The study showed the proportion of taxa identified at different taxonomic levels. The decrease at the species level in 16S rDNA-based studies is due to the fact that many species do not differ in the selected variable regions of the gene. According to the metagenomic analysis results, the dominant bacterial species for milk kefir were determined to be Lactobacillus helveticus and Lentilactobacillus parakefiri, while for water kefir they were Liquorilactobacillus nagelii, Liquorilactobacillus satsumensis, Liquorilactobacillus ghanensis, and Lentilactobacillus parakefiri. Since the starter cultures formed from these grain structures are traditionally produced, they are very different from each other. These differences stem from the different raw materials they use, or from contaminations, equipment, and production parameters during the production stage. The bacterial species that create the differences in the obtained data contribute to the literature.