Effect of autoinducer-2 on biofilm formation of mixed strains derived from kefir.

The mechanisms underlying kefir grain formation remain to be elucidated. Quorum sensing is a new direction for investigating this process. To explore the formation mechanism of kefir grain through quorum sensing, it is first necessary to establish its association with kefir grain formation. As biofilm constitutes the foundation of the extracellular matrix in kefir grains, this study focused on its relationship with quorum sensing. Three lactic acid bacteria, one yeast, and one acetic acid bacteria with strong biofilm-forming abilities were isolated from kefir and were cultured in pairwise and three-strain mixed cultures. The results revealed a strong correlation between autoinducer-2 secretion and biofilm formation, with both displaying similar trends under various culture conditions. Optimal biofilm formation and autoinducer-2 production were observed at 4 h, 37 °C, and pH 7.5. Under these conditions, the three-strain mixed culture exhibited the highest autoinducer-2 fluorescence intensity (6.45 ± 0.27), and biofilm quantity reached 3.83 ± 0.094. Notably, biofilm formation and autoinducer-2 secretion were lower in the same-strain cultures than in the mixed-strain cultures. This study is the first to establish a strong link between quorum sensing and kefir grain formation.