Showcase of Undergraduate Research and Creative Endeavors (SOURCE)

Isolating, Purifying, and Investigating Mycobacterial Lysogens

Bacteria have shared an entangled evolutionary history with bacteriophages for the past three billion years. Some bacteriophages use a specific type of infectious pathway (lysogeny) that maintains their hosts’ viability, thus enabling a mechanism of coexistence. In certain phage genomes, annotation has revealed the presence of immunity-related genes, which suggests a mechanism of how some bacteriophages can protect their hosts and resist superinfection by other related bacteriophages. To investigate this further, two temperate (and previously annotated) mycobacteriophages (ExplosioNervosa and Rhynn) were isolated in an effort to create lysogens in their host cell, Mycobacteria smegmatis. Once created, the lysogens were purified and tested against their original infecting phage as well as an unrelated bacteriophage (Haimas) to see if they were able to resist superinfection. Tests showed that both Haimas and the original viruses were still able to infect the lysogens and cause them to lyse. The ability of bacteriophages to lyse their own lysogens raised the idea of spontaneous reversion: the prophages could have reverted to the lytic cycle due to a triggering condition in their environment. The ability of the host—phage relationship to respond to certain environmental signals warrants further investigation, as does manipulation of the genes linked with immunity and infection. Investigating the triggers and unraveling the mechanisms that fuel coevolution help further our understanding of the host—parasite equilibrium that exists today and highlights opportunities for future applications.