Identification of cell wall proteins of Bacteroides fragilis to which bacteriophage B40-8 binds specifically

Bacteriophage infecting Bacteroides fragilis, one of the most abundant bact eria in the human colon, have been proposed as indicators of virological fa ecal pollution, The first identification of a receptor for a bacteriophage in B. fragilis is reported here, First, resistant mutants were characterize d following phage inactivation, and it was shown that cell wall proteins ar e involved in phage binding, Then the proteins involved were identified by various approaches: (i) comparison of the protein profiles of wild-type B, fragilis HSP40 and phage-resistant mutants; (ii) application of a modificat ion of the virus overlay protein blot assay (VOPBA), At least two proteins of B. fragilis, with apparent molecular masses of 35 +/- 5 kDa and 65 +/- 5 kDa, bind to B40-8. This result was later confirmed by running a complex c onsisting of this phage bound to radiolabelled proteins of B. fragilis on a n immunoaffinity column loaded with a specific antibody against the phage, Cell proteins retained in the column also coincided with the proteins that differed in the profiles of resistant mutants. Finally, to identify the pot ential function of these two proteins, their N-terminal sequences were dete rmined and compared to published sequences, but no homologies were found.