| Surface layer(S-layer) proteins cover the entire outermost cell surface of many bacteria and Archaea. They can form well-distributed, porous, monomolecular crystalline arrays by self-assembly. The investigation into the connection between S-layer proteins and probiotic properties of strains has become a popular research topic. The influence of S-layer proteins on surface properties, tolerance to gastric and small intestinal juices, adhesion properties of lactobacilli and adhesion properties of pathogens was investigated. The results may provide a theoretical basis for more in depth work on the relationship between S-layer proteins and lactobacillar probiotic functions.SDS-PAGE results showed that three S-layered strains, Lactobacillus acidophilus FB11、L. gasseri FB8、L. casei zhang, were screened with the reference strain, L. acidophilus NCFM. The molecular masses of three Lactobacillus S-layer proteins were 44 k Da, 45 k Da, 43 k Da, respectively.HPLC analyses resulted that the hydrophobic amino acids contents of S-layer proteins from L. acidophilus NCFM L. acidophilus FB11、L. gasseri FB8、L. casei zhang were 35.31%, 39.67%, 44.69%, 49.06% while the basic amino acids contents were 13.58%, 20.57%, 22.88%, 12.19%, respectively. CD analyses showed that the contents of α-helix were 33.7%, 34.3%, 24.1%, 43.5% while the contents of β-sheet were 13.6%, 11.7%, 20.8%, 16.0%, respectively. The thermal denaturation temperatures analyzed by DSC were 65.10±0.16 oC, 64.17±0.83 oC, 70.51±0.54 oC, 59.53±0.58 oC, respectively.Surface properties analyses resulted that after removing S-layer proteins by Li Cl treatment, the four lactobacilli showed a significant decline(P < 0.05) in the autoaggregation, coaggregation with Escherichia coli / Salmonella typhimurium, surface hydrophobicity and surface charge. It suggested that S-layer proteins contributed to the surface properties of strains positively, and were beneficial to the nonspecific adhesion and clearance of pathogens. Tolerance analyses resulted that the four lactobacilli without S-layer proteins exhibited a significant decline(P < 0.05) in the tolerance to gastric and small intestinal juices. The tolerance to gastric juice of L. gasseri FB8 decreased by 56% while the tolerance to small intestinal juice decreased by 72%, higher than other three lactobacilli. It indicated that S-layer proteins provided strains with protection, maintained the viability of strains in gastrointestinal tract and benefited the exertion of probiotic functions.Adhesion properties analyses showed that the four lactobacilli without S-layer proteins exhibited a significant decline(P < 0.05) in the adhesion to type I collagen(Cn I), type V collagen(Cn V) and HT-29 cells. For adhesion to Cn I, the adhesion of L. gasseri FB8 decreased by 95%, higher than that of other three lactobacilli; for adhesion to Cn V, the adhesion of L. acidophilus FB11 decreased by 75%, higher than that of other three lactobacilli; for adhesion to HT-29 cells, the adhesion of L. acidophilus NCFM decreased by 82%, higher than that of other three lactobacilli. It suggested that S-layer proteins participated in the adhesion of strains to extracellular matrix proteins and intestinal epithelial cells, helped lactobacilli colonize the intestinal tract and were beneficial to exert probiotic properties further.Furthermore, anti-adhesion analyses showed that the four S-layer proteins inhibited the adhesion of pathogens to Cn I, Cn V and HT-29 cells effectively, exhibiting good anti-adhesion property. S-layer proteins were helpful for inhibiting the adhesion of pathogens to extracellular matrix proteins and intestinal epithelial cells.In conclusion, the four tested S-layer proteins had a positive influence on the lactobacillar surface properties, tolerance to gastric and small intestinal juices and adhesion properties, and behaved an inhibitory effect on the adhesion of pathogens. These will benefit the exertion of lactobacillar probiotic functions in the intestinal tract of humans and animals. |
PDF Full Text Request