Expansion of enterococcal insertion sequence elements during bacteriophage infection

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PROJECT SUMMARY Multidrug resistant enterococcal infections are a serious public health threat. The enterococci, including Enterococcus faecalis, often harbor resistance to critical front-line drugs such as ampicillin and/or vancomycin. Due to the increasing difficulty of treating enterococcal infections with currently available drugs, alternative treatment options are needed. One possibility is the therapeutic use of bacterial viruses known as bacteriophages (phages). While phage therapy has shown promise in the clinic, the emergence of phage resistance in bacteria is a serious concern for future phage therapies. To overcome this, we need to understand how bacteria respond to phage infection at the genetic level and the physiological consequences of phage resistance. Past work in our lab discovered that E. faecalis isolates resistant to lytic phage 19 (phi19) infection harbored an increased number of IS256 transposable element insertions in their genomes. These insertions were commonly found in genes involved in phage infection, suggesting that phi19 infection stimulates IS256 transposition to create new genetic combinations, leading to phage resistance. My preliminary work has demonstrated that phi19 infection activates IS256 mobilization. I have found that phi19 infection increases the translation of the IS256 transposase, and that a phi19-encoded transcription factor that resembles an anti-sigma factor, termed PAS19, increases IS256 transposase translation. This indicates that PAS19 is responsible for activating IS256 during phi19 infection. The goals of this project are to decipher how the E. faecalis genome evolves in response to phage driven IS256 activation, and how these downstream effects can inform phage therapeutic strategies. To achieve these goals, I will execute two specific aims: Aim 1: Establish a mechanistic basis for phage-induced expansion of IS256 insertions in E. faecalis. Work performed in this aim will demonstrate the functional enzymatic requirements and timing of phage mediated IS256 activation, and will determine if this activity is broadly applicable to diverse enterococcal phages; Aim 2: Determine how a putative phage transcription factor controls IS256 activation. PAS19, a putative transcription factor encoded by phi19 activates IS256 expression. In this aim, I will delineate how PAS19 controls IS256 gene activation.