CHARACTERIZATION OF THE AGGREGATION PROMOTING FACTOR FROM LACTOBACILLUS-GASSERI, A VAGINAL ISOLATE

Lactobacillus gasseri 2459, isolated from the human vagina, exhibits a strong autoaggregating phenotype. Filter-sterilized spent supernatant s of this strain promote aggregation of Lact. plantarum LL441 and Ente rococcus faecalis EF. Aggregation was abolished upon exposure of the c ells to proteases and, in the case of Ent. faecalis, to metaperiodate, which suggests the involvement of cell-surface proteins and glycoprot eins, respectively, in the aggregation phenotype. In accordance with t his, a 75 kDa surface protein, and possibly another of approximately 9 4 kDa, appears in Lact. plantarum LL441 cultures incubated with Lact. gasseri culture supernatants. The diffusible aggregation promoting fac tor was purified from stationary phase culture supernatants and determ ined to be a 2 kDa hydrophilic peptide active at pH 3-4 and stable at neutral and acid pH. The activity was resistant to heat, chymotrypsin, chelating agents, triton X-100 and reducing agents, but sensitive to other proteases and SDS.