Introducing Casbah, Kronus, and MmasiCarm, Members of the Mycobacteriophage Subcluster B3

Background: As part of a large science education effort, bacteriophages that lyse Mycobacterium smegmatis mc²155 continue to be discovered.

Materials and methods: Phages were isolated from soil samples from urban sites in the Northeastern United States. Their genomes were sequenced, assembled, and bioinformatically compared.

Results: Three lytic siphoviruses belonging to subcluster B3 with high similarity to each other and other B3 mycobacteriophages were isolated. These phages contain double-stranded DNA genomes (68,754 to 69,495 bp) with high GC content (67.4-67.5%) and 102-104 putative protein coding genes. Notable features include a HicA-like toxin and 33 genes exclusive to subcluster B3. One phage had an intein in its terminase sequence.

Conclusions: Genomic analyses of these phages provide insights into genome evolution and horizontal gene transfer (HGT). The networks for HGT are apparently vast and gene specific. Interestingly, a number of genes are found in both B3 and Gordonia DR phages.