Comparative analysis of the genomes of mycobacteriophages infecting saprophytic and pathogenic mycobacteria.

The genomes of a series of mycobacteriophages have been analyzed to disclose possible relationships between genetic characteristics and host range. The percent guanine-plus-cytosine in the DNA of 14 phages was found to be 34.4 to 47.5, as determined by a double-labelling procedure, which is unaffected by the presence of modified bases. The DNA of few mycobacteriophages yielded discordant values when the G + C content was estimated by buoyant density determination and by the double labelling procedure. This observation suggests the possible presence of modified bases in these genomes. The reduced susceptibility of viral DNAs to several restriction endonucleases is suggestive of the occurrence of both methyladenine and methylcytosine in the genome of all the mycobacteriophages studied. Heterologous annealing among the 14 DNAs analyzed yielded 6 hybridization groups. Within one group, the homology level among viral genomes was estimated by comparing the electrophoretic mobilities of restriction fragments: values of 0.8 to 1.3% base substitution have thus been found. A comparison of the genomic characteristics and host range of the mycobacteriophages analyzed suggests a possible relationship between restriction pattern, G + C content, crosshybridization level and host range.