The heterogenous and diverse population of prophages in Mycobacterium genomes

Abstract

Bacterial genomes commonly carry one or more integrated prophages, although prophage prevalence varies greatly in different bacterial genera and species. We have used the recently developed DEPhT software to discover prophages present in sequenced Mycobacterium genomes. Prophages are unevenly distributed among mycobacteria; Mycobacterium tuberculosis strains are devoid of intact prophages, whereas 75% of Mycobacterium abscessus-chelonae strains carry at least one prophage, and some have up to nine. Newly discovered prophage sequences are generally distinct from those of lytic phages isolated using Mycobacterium smegmatis as a host, although assembly of over 3,800 phage and prophage genomes into clusters based on shared sequence similarity yields seven clusters containing both phage and prophage genomes. M. abscessus prophages use a usually large repertoire of attB sites for prophage integration, and new integration-proficient vectors demonstrate the functionality of integration systems identified in silico and provide tools useful for advancing M. abscessus genetics. Genomic analysis reveals additional accessory and likely mobile parts of Mycobacterium genomes including defective prophages, prophage-like regions, and satellite elements proposed to be candidate phage-inducible chromosomal islands (PICIs). M. abscessus prophages and PICIs are unusual in that they often encode phage-encoded ESX-secreted toxin (PEST) systems that are located adjacent to the phage integration functions and are lysogenically expressed and likely provide a fitness advantage to their host. Mycobacterium species include several human pathogens and mycobacteriophages show potential for therapeutic use to control Mycobacterium infections. However, phage infection profiles vary greatly among Mycobacterium abscessus clinical isolates and phage therapies must be personalized for individual patients. Mycobacterium phage susceptibility is likely determined primarily by accessory parts of bacterial genomes, and we have identified the prophage and phage-related genomic regions across sequenced Mycobacterium strains. The prophages are numerous and diverse, especially in M. abscessus genomes, and provide a potentially rich reservoir of new viruses that can be propagated lytically and used to expand the repertoire of therapeutically useful phages.