Trigger Factor, Mycobacterium tuberculosis' Double-Edged Sword: Immunity to a Mycobacteriophage at the Cost of Virulence

Abstract

The struggle for survival between phages and their bacterial hosts is best exemplified by the diverse mechanisms bacteria utilize to block phage infection, and the methods phages use to surmount them. Mycobacteriophage DS6A is unique amongst the more than 8000 identified mycobacteriophages in that its host range is restricted to mycobacteria that are members of the Mycobacterium tuberculosis Complex (MTBC). However, the molecular mechanism for this specificity remains unknown. To study the relationship DS6A has to both MTBC and non-tuberculous mycobacteria (NTMs), we generated two novel recombinant DS6A shuttle phasmids containing fluorescent reporter mVenus. These phages were utilized to clearly demonstrate that 50 years of previous scientific dogma was incorrect, and DS6A can in fact infect NTM mycobacteria to a wide range of degrees. Work teasing out the mechanisms of resistance is underway. Additionally, we identified the chaperone trigger factor (Tig; Rv2462c) to be required for a productive DS6A infection in Mtb. Interestingly, no host range mutants have been generated that can overcome this resistance to plaguing. Deleting tig did not affect the lysis profile of any of the other >30 mycobacteriophages able to infect Mtb. Susceptibility of Mtb Delta tig to DS6A infection was rescued by complementation of tig on an integrating plasmid. DS6A fluorophage infection of Mtb Delta tig induced high levels of detectable fluorescence, suggesting Tig is not required for the adsorption of phage or introduction of DS6A DNA. Additionally assays determined that Tig was not involved in transcriptional or translational activation. However, deleting tig did yield an additional phenotype in Mtb; significant attenuation in both immunocompetent and immunocompromised mice. Lipidome and secretome assays showed stark differences between the lipid makeup and secreted protein profiles of the tig mutant versus the WT that could explain the cause of attenuation. For Mtb, the loss of tig is a double edged sword; total resistance to DS6A is afforded in the clonal population, but at the cost of virulence in eukaryotic hosts.