Investigating the role of RNase HI in antibiotic susceptible Mycobacteria

Abstract

Antibiotic resistance generated by the SOS response is a major challenge when treating microbial infections. Inhibition of RecA, the master regulator of the SOS response, is validated as an anti-mutagenic target, but only when paired with an SOS-inducing antibiotic like ciprofloxacin. When one of the two copies the essential R-loop resolving endonuclease RNase HI is knocked out in Mycobacterium smegmatis, the SOS response is upregulated. I hypothesise that this may have the effect of enhancing mutagenesis and the acquisition of resistance. We show that RNase HI inhibition will synergize with RecA inhibition using suramin and zinc in M. smegmatis, enhancing cell killing. As Mycobacterium tuberculosis, the causative agent of tuberculosis, requires RNase HI, targeting it will allow us to identify optimal antibiotic combinations, and to determine whether combined RNase HI and RecA inhibition will act synergistically to prevent resistance. To investigate this, we will determine the mutagenesis rate of RNase HI deficient M. smegmatis, and probe these strains under a variety of conditions, such as hypoxia, RecA inhibition, and antibiotic exposure to determine susceptible phenotypes that improve the efficacy of killing or prevent mutagenesis. RNase HI inhibition as a target for tuberculosis, alongside SOS response inhibition, has potential as a component of future combination therapy to induce antibiotic sensitivity in mycobacteria.