An exoproteome approach to monitor safety of a cheese-isolated Lactococcus lactis

The safety of the cheese-isolated and potential starter Lactococcus lactis 11D was explored by means of an extracellular proteomic study. A preliminary analysis showed good caseification/proteolytic behavior of the strain, absence of production of biogenic amines and good survival at acidic pH. The extracellular proteome map was analyzed to investigate the presence of potential virulence factors. Five moonlighting proteins with adhesive properties (ornithine carbamoyltransferase, fructose bisphosphate aldolase, trigger factor, EF-Tu and GroEL) were identified in the exoproteome, as well as the potential plasminogen binding proteins enolase, GAPDH and phosphoglycerate mutase. Adhesive properties are fundamental features for good starters and commensal strains, although some controversial aspects arise from plasminogen binding proteins as we shall discuss. Noticeably, GroEL, chitinase, and triose phosphate isomerase were abundant in the L. lactis 11D exoproteome. These proteins play a role in bacterial aggregation and in bacteria-fungi interactions, therefore their presence may indicate a good competition potential of the strain against other microorganisms in both food and the gastrointestinal habitat. A DIGE comparative exoproteomic analysis was performed on the L. lactis 11D strain grown on glucose and the disaccharide trehalose, examined here due to its common use as lyophilization stabilizer, respectively. The experiment showed that chitinase biosynthesis was enhanced in presence of trehalose. This is to our knowledge the first extracellular proteomic mapping of L. lactis with relevance for bacterial strain-typing in food safety.