Abstract:
Water kefir consists of a symbiotic association of different bacteria and yeasts embedded in polysaccharide grains, which ferment a sucrose solution supplemented with dried fruits to a tasty beverage. Different consortia harbor microbiomes comprising a similar metabolic core delivering beverages with similar content of major metabolic compounds. Based on limited nitrogen content in water kefir medium, isolates compete for it and rely on support of each other. Co-cultivation experiments with yeasts and lactobacilli isolated from water kefir delineates mutualism in water kefir. Enhanced formation of metabolites and glycolytic proteins demonstrates the increasing metabolic activity of single organisms during co-cultivation. Lactobacilli optimize the physical environment for Zygotorulaspora florentina while acidifying the milieu. Co-cultivated yeasts are induced to supply amino acids and vitamins, which are essential for lactobacilli.