Bacteriophage taxonomy

Abstract

Bacteriophages or ?phages? are viruses of prokaryotes. At least 5,360 tailed and 179 cubic, filamentous, and pleomorphic bacterial viruses have been examined in the electron microscope since the introduction of negative staining in 1959. Since at least 100 novel bacterial viruses are described every year1, the approximate number of viruses under consideration is over 6,000. Numerically, this makes bacteriophages the largest virus group known. Phages are presently classified in a hierarchical and holistic system with one order and 10 families. Over 96% of phages are tailed and contain dsDNA. The seven families of cubic, filamentous and pleomorphic phages are small and well defined. They contain ds or ss DNA or RNA. The most important developments are reclassifications of the Podoviridae and Myoviridae families of tailed phages.