Interspecies Protection against Freezing Stress within a Food Microbial Community

This study was completed on an artificial microbial community (consortium) including three microorganisms of dairy interest, two mesophilic (Lactococcus lactis subsp. cremoris and Geotrichum candidum) and one thermophilic (Lactobacillus delbrueckii subsp. bulgaricus). The aim of this work was to study the stress responses of the food microbial consortium subjected to a freeze–thaw challenge (–20°C, 10 min / +25°C, 3 min) combined with physiological cryoadaptation (cryotolerance). Our results show that induction of cryotolerance by near-freezing temperature pretreatment of G. candidum and L. cremoris within the microbial community is similar to the one obtained with pure cultures. However, cryotolerance of L. bulgaricus was only induced within the consortium in milk. An interspecies cryoprotection was thus identified. This acquisition is correlated with the cell envelope extracts of G. candidum and/or the extracellular fractions of the two adapted mesophilic microorganisms. Therefore, in our experimental conditions, G. candidum and L. cremoris are both, in co-cultures, necessary to obtain optimal cryoprotection of L. bulgaricus.