Cooperation between species in the yogurt consortium is affected by the modulation of intracellular pH that is driven by Streptococcus thermophilus urease activity

The proto-cooperation between Streptococcus thermophilus and Lactobacillus delbrueckii subsp. bulgaricus in the yogurt consortium enhances the growth rate and size of each population. In contrast, the independent growth of the two species in milk leads to a slower growth rate and a smaller population size (1, 2). In this study, we report the first evidence that the urease activity of S. thermophilus interferes with the intracellular pH of L. delbrueckii, modulating the bioenergetics of this species during milk fermentation.