Fermentation is one of the most effective methods of food preservation. Since ancient times, food has been fermented using lactic acid bacteria (LAB). Fermented milk is a very intricate fermentation ecosystem, and the microbial metabolism of fermented milk largely determines its metabolic properties. The two most frequently used dairy starter strains are Streptococcus thermophilus (S. thermophilus) and Lactobacillus delbrueckii subsp. bulgaricus (L. bulgaricus). To enhance both the culture growth rate and the flavor and quality of the fermented milk, it has long been customary to combine S. thermophilus and L. bulgaricus in milk fermentation due to their mutually beneficial and symbiotic relationship. On the one hand, the symbiotic relationship is reflected by the nutrient co-dependence of the two microbes at the metabolic level. On the other hand, more complex interaction mechanisms, such as quorum sensing between cells, are involved. This review summarizes the application of LAB in fermented dairy products and discusses the symbiotic mechanisms and interactions of milk LAB starter strains from the perspective of nutrient supply and intra- and interspecific quorum sensing. This review provides updated information and knowledge on microbial interactions in a fermented milk ecosystem.
Keywords: Fermented milk; Lactobacillus delbrueckii subsp. bulgaricus; Streptococcus thermophilus; lactic acid bacteria; nutrient co-dependence; quorum sensing; symbiosis.
The symbiotic relationship between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus is reviewed.Their nutrient co-dependence is discussed.The role of quorum sensing in their interaction is discussed for the first time.This review is of interest to colleagues interested in exploiting LAB starter cultures.