Mycobacteriophages – more diverse than expected

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It’s the Phestival of Phage 2011 on MicrobiologyBytes :-)

Bacteriophage animation Bacteriophages are the most numerous biological entities in the biosphere, with an estimated 1031 particles. The global population is highly dynamic with an estimated 1023 phage infections per second, and has likely been evolving for perhaps two to four billion years. Not surprisingly, this has given rise to a genetically highly diverse population. Most bacteriophages do not extend their host range beyond a single bacterial genus, and host specificity likely offers a substantial impediment to the free exchange of genetic material between phages of different bacterial hosts. Consequently, it is unusual to find extensive nucleotide sequence similarity among phages of different hosts; such phages often share few if any genes identifiable through amino acid sequence comparisons.

Remarkably, phages capable of infecting a single bacterial species can also be highly diverse, as are for example the genetically distinct DNA phages of Escherichia coli, such as φX174, M13, lambda, T1, T4, T5, and T7. This is further exemplified with the mycobacteriophages – viruses infecting mycobacterial hosts – of which sixty-two genomes of phages known to infect Mycobacterium smegmatis mc2155 have been sequenced. All of these are dsDNA tailed phages, restricted to two morphotypes, the Siphoviridae and the Myoviridae.

This paper describes the isolation and characterization of new mycobacteriophages by student microbiologists, a valuble contribution to our understanding of these organisms.

Expanding the Diversity of Mycobacteriophages: Insights into Genome Architecture and Evolution. (2011) PLoS ONE 6(1): e16329. doi:10.1371/journal.pone.0016329
Mycobacteriophages are viruses that infect mycobacterial hosts such as Mycobacterium smegmatis and Mycobacterium tuberculosis. All mycobacteriophages characterized to date are dsDNA tailed phages, and have either siphoviral or myoviral morphotypes. However, their genetic diversity is considerable, and although sixty-two genomes have been sequenced and comparatively analyzed, these likely represent only a small portion of the diversity of the mycobacteriophage population at large. Here we report the isolation, sequencing and comparative genomic analysis of 18 new mycobacteriophages isolated from geographically distinct locations within the United States. Although no clear correlation between location and genome type can be discerned, these genomes expand our knowledge of mycobacteriophage diversity and enhance our understanding of the roles of mobile elements in viral evolution. Expansion of the number of mycobacteriophages grouped within Cluster A provides insights into the basis of immune specificity in these temperate phages, and we also describe a novel example of apparent immunity theft. The isolation and genomic analysis of bacteriophages by freshman college students provides an example of an authentic research experience for novice scientists.

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