Positive interactions between lactic acid bacteria promotedby nitrogen-based nutritional dependencies

International audienceLacticacidbacteria(LAB)interactionsareoftenstudiedinassociationwithyeastsorpropionibacteria in various fermented food products and the mechanisms underlying theirinteractions are being quite well characterized. Concerning interactions between LAB, whichareresponsibleforthesanitary,organoleptic,andhealthpropertiesofmostfermentedproducts,they have mainly been investigated to test antagonistic interactions. Understanding how theycan positively interact could be useful in multiple food-related fields: production of fermentedfood products with enhanced functional properties or fermentation of new food matrices.Nutritionaldependencies,especiallythoseregardingnitrogensources,governnumerousmicrobial positive interactions. As for LAB, such positive interactions, have previously beenstudied between yogurt bacteria. However, they have never been exploited to create artificialco-culturesofLABthatwouldnotnecessarilycoexistnaturally,i.efromdifferentbiotopes.TheobjectiveofthisstudywastopromoteLABpositiveinteractionsbasedonnitrogendependencies in co-cultures to increase acidification rates, carbohydrate consumption, andvolatilecompoundproduction.Thestrategywastoexploitbothproteolyticactivitiesandaminoacid auxotrophies of LAB.A chemically defined medium was thus developed to specificallyallow the growth of six LAB strains used, three proteolytic and three non-proteolytic. Each oftheproteolyticstrains,EnterococcusfaecalisCIRM-BIA2412,LactococcuslactisNCDO2125,andCIRM-BIA244,wasco-culturedwitheachoneofthenon-proteolyticLABstrains:L.lactisNCDO2111, LactiplantibacillusplantarumCIRM-BIA465and CIRM-BIA1524.Bacterialgrowth was monitored using compartmented chambers to compare growth in mono-and co-cultures. Acidification,carbohydrateconsumption and volatilecompound production wasevaluated in direct co-cultures. Each proteolytic strain induced different types of interactions:eitherstronglypositive,weaklypositive,ornointeractions,withE.faecalisCIRM-BIA2412,L. lactisNCDO2125 andL. lactisCIRM-BIA244, respectively. Strong interactions wereassociatedwithhigherconcentrationsintryptophan,valine,phenylalanine, leucine,isoleucine,and peptides. They led to faster acidification rates, lower final pH, higher raffinose utilization,andhigher concentrations in fivevolatilecompounds