Genomic structure of phage B40-8 of Bacteroides fragilis

Very few data are available on the molecular biology of Bacteroides fragili s bacteriophages, which have been considered in several studies as indicato rs of faecal contamination. Phage B40-8, initially isolated from an urban s ewage sample using a strain of B. fragilis (HSP40) isolated from a clinical specimen, was chosen in this study as a prototype for morphological and mo lecular studies. Like most of the phages infective for B. fragilis. B40-8 b elongs 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 p ercentage (38.9 mol%) of G+C. The ends of the molecule appeared not to be c ohesive but permuted, with a terminal redundancy of 7.3 %. A genomic map wa s constructed. Three major proteins (MP) out of 15 peptides in the SDS-PAGE profile were selected for N-terminal sequencing. From these data, degenera te probes were designed to locate the ORFs in the genomic map. Immunodetect ion by electron microscopy revealed that MP1 and MP3 were structural protei ns 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 id entified and sequenced.