This work was aimed at investigating the molecular mechanisms of Quorum Sensing (QS) in Lactobacillus plantarum DC400 when co-cultured with other sourdough lactobacilli. The growth and survival of L. plantarum DC400 was not affected when co-cultivated with Lactobacillus sanfranciscensis DPPMA174 or Lactobacillus rossiae A7. Nevertheless, 2-DE analysis showed that the level of protein expression of L. plantarum DC400 increased under co-culture conditions. Although several proteins were commonly induced in both co-cultures, the highest induction was found in co-culture with L. rossiae A7. Overexpressed proteins, related to QS and stress response mechanisms, were identified: DnaK, GroEL, 30S ribosomal protein S1 and S6, ATP synthase subunit beta, adenosylmethionine synthetase (MetK), phosphopyruvate hydratase, phosphoglycerate kinase, elongation factor Tu, putative manganese-dependent inorganic pyrophosphatase, d-lactate dehydrogenase, triosephosphate isomerase, fructose-bisphosphate aldolase and nucleoside-diphosphate kinase. As shown by real-time PCR, expression of the luxS gene of L. plantarum DC400 was also affected during co-cultivation. According to overexpression of MetK and luxS during co-cultivation, synthesis of AI-2-like substances was also influenced by the type of microbial co-cultures. This study showed that expression of some genes/proteins, also QS-related, in L. plantarum was influenced by co-cultivation of other sourdough lactobacilli.