Genomic structure of phage B40-8 of Bacteroides fragilis

Very few data are available on the molecular biology of Bacteroides fragilis bacteriophages, which have been considered in several studies as indicators of faecal contamination. Phage B40-8, initially isolated from an urban sewage sample using a strain of B. fragilis (HSP40) isolated from a clinical specimen, was chosen in this study as a prototype for morphological and molecular studies. Like most of the phages infective for B. fragilis, B40-8 belongs to the Siphoviridae family. Its genome has been found to be a double-stranded DNA molecule, of approximately 51·7 kb, containing a rather low percentage (38·9 mol%) of G+C. The ends of the molecule appeared not to be cohesive but permuted, with a terminal redundancy of 7·3%. A genomic map was constructed. Three major proteins (MP) out of 15 peptides in the SDS-PAGE profile were selected for N-terminal sequencing. From these data, degenerate probes were designed to locate the ORFs in the genomic map. Immunodetection by electron microscopy revealed that MP1 and MP3 were structural proteins of the phage head and that MP2 was a constituent of the tail. A genomic library of the phage was prepared, and a clone including the MP2 ORF was identified and sequenced.