Resistance is Phutile - Using Host Cell Mutants to Advance Our Understanding of Phage Gene Function
Dr. Virgina McDonough and Dr. Joseph Stukey
Mycobacteriophages are viruses that infect members of the bacterial genus Mycobacterium. With over 330 mycobacteriophage genomes sequenced and available in GenBank, they are the largest collection of sequenced phages that infect a single host (Mycobacterium smegmatis). Comparative genomic analysis reveals that mycobacteriophages are very diverse with more than 25 genetically distinct “types.” Collectively, they possess numerous genes that encode novel proteins that have yet to be studied. Some of these novel proteins are predicted to have a role in targeting critical host cell processes during phage infection and promoting new phage production. To identify phage genes that may target critical host cell processes, individual genes or small genomic segments containing only a few genes were expressed in M. smegmatis and effects on cell growth (cytotoxicity) were observed. Using this approach, we have identified several cytotoxic genes or gene segments in two genetically unrelated phages, Vix (gene or gene segments: 65-66, 68-72, 80, and 87-88) and Pumpkin (gene or gene segments: 115, 119, 142 and 143). In an effort to identify relevant host cell targets, we have initiated a genetics approach and present here our initial characterization of spontaneous and chemically induced mutant strains of M. smegmatis that are resistant to specific cytotoxic phage genes. We reason that at least some of the resistant M. smegmatis strains will have mutations in the genes that are the targets of the mycobacteriophages. Subsequent identification of the mutated host cell genes will provide important information on the nature of the interactions involving mycobacteriophages and their host, M. smegmatis.
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