Lactic acid bacteria (LAB) interactions are often studied in association with yeasts or propionibacteria in various fermented food products and the mechanisms underlying their interactions are being quite well characterized. Concerning interactions between LAB, which are responsible for the sanitary, organoleptic, and health properties of most fermented products, they have mainly been investigated to test antagonistic interactions. Understanding how LABcan positively interact could be useful in multiple food-related fields, e. g. production of fermented food products with enhanced functional properties,or fermentation of new food matrices. Nutritional dependencies, especially those regarding nitrogen sources, govern numerous microbial positive interactions. As for LAB, such positive interactions have mainlybeen studied between yogurt bacteria. However, they have never been exploited to create artificial co-cultures of LAB that would not necessarily coexist naturally, i.efrom different biotopes. The objective of this study was to promote LAB positive interactions based on nitrogen dependencies in co-cultures to increase acidification rates, carbohydrate consumption, and volatile compound production. The strategy was to exploit both proteolytic activities and amino acid auxotrophies of LAB. Material and methodsA chemically defined medium was thus developed to specifically allow the growth of the six LAB strains chosen, three proteolytic and three non-proteolytic. Each of the proteolytic strains, Enterococcus faecalis CIRM-BIA2412, Lactococcus lactisNCDO2125, and CIRM-BIA244, was co-cultured with each one of the non-proteolytic LAB strains: L. lactisNCDO2111, Lactiplantibacillus plantarumCIRM-BIA465 and CIRM-BIA1524. Bacterial growth was monitored using compartmented chambers andcomparedin mono-and co-cultures. Acidification, carbohydrate consumption and volatile compound production were also investigated.Results and discussionEach proteolytic strain induced different types of interactions: either strongly positive, weakly positive, or no interactions, with E. faecalisCIRM-BIA2412, L. lactisNCDO2125 and L. lactisCIRM-BIA244, respectively, regardless the non-proteolytic strain associated. Strong interactions were associated with higher concentrations in tryptophan, valine, phenylalanine, leucine, isoleucine, and peptides. They led to faster acidification rates, lower final pH, higher raffinose utilization, and higher concentrations in some volatile compounds