Enhancement of probiotic activity by S-layer protein of Lactobacillus plantarum D6 strain in coculture with L. plantarum D13

Among numerous lactic acid bacteria strains isolated from autochthonous smoked fresh cheeses, potential probiotic strains were selected according to strict probiotic selection criteria. Further research revealed that the strain MCD6 was actually a coculture of two Lactobacillus plantarum strains which were identified as L. plantarum D13 and L. plantarum D6, where L. plantarum D6 expresses surface S-layer proteins of approximately 45 kDa. Since S-layer proteins, to our knowledge, have never been identified among representatives of L. plantarum species, it was of our great interest to further characterise and study its functional role in probiotic activity. Hence, the S-layer functional role in probiotic activity of coculture L. plantarum D6 and L. plantarum D13 through the comparison of important functional activities of probiotic strains was evaluated. Aggregation and coaggregation abilities, adhesion to intestinal epithelial cells in vitro, pathogen exclusion and survival in simulated conditions of gastrointestinal tract and during freeze drying, before and after guanidine hydrochloride extraction of S-layer proteins were examined in coculture and monocultures of L. plantarum D13 and L. plantarum D6, respectively. As a result it was established that coculture of two L. plantarum strains enhances their probiotic activity due to the S-layer protein of L. plantarum D6 strain.