Microviridae, a family divided: Isolation, characterization, and genome sequence of φMH2K, a bacteriophage of the obligate intracellular parasitic bacterium Bdellovibrio bacteriovorus

A novel single-stranded DNA phage, φMH2K, of Bdellovibrio bacteriovorus was isolated, characterized, and sequenced. This phage is a member of the Microviridae, a family typified by bacteriophage φX174. Although B. bacteriovorus and Escherichia coli are both classified as proteobacteria, φMH2K is only distantly related to φX174. Instead, φMH2K exhibits an extremely close relationship to the Microviridae of Chlamydia in both genome organization and encoded proteins. Unlike the double-stranded DNA bacteriophages, for which a wide spectrum of diversity has been observed, the single-stranded icosahedral bacteriophages appear to fall into two distinct subfamilies. These observations suggest that the mechanisms driving single-stranded DNA bacteriophage evolution are inherently different from those driving the evolution of the double-stranded bacteriophages.