There is also considerable range in overall guanine plus cytosine content (GC%), from 50.3% to 70%, with an average of 64% ("M. smegmatis" is 67.3%). Thus, phage GC% does not necessarily match that of its host, and the consequent mismatch of codon usage profiles does not appear to be detrimental. Because new mycobacteriophages lacking extensive DNA similarity with the extant collection are still being discovered, and as there are at least seven singletons for which no relatives have been isolated, we clearly have yet to saturate the diversity of this particular population.