Just thought I would just do a quick post on a really interesting paper, ‘A bacteriophage encodes its own CRISPR/Cas adaptive response to evade host innate immunity’. Briefly summarised below…
Vibrio cholera is in a dynamic relationship with phage – walking a tight rope between increasing phage resistance and decreasing virulence. There is an evolutionary tussle over the O1 antigen, mutations in the O1 antigen allow it to escape phage predation but expression of the O1 antigen is a major virulence determinant.
V. cholera has therefore evolved other phage defenses to allow it to maintain O1 antigen display. These defenses include the Phage Induced Chromosomal Island (PICI), an 18 kb island encoding various mechanisms of phage resistance. This island has been seen in both V. cholera, and prototypically in S. aureus. Transcription from these regions is induced upon phage interaction, resulting in phage resistance.
A diverse array of bacteria encode CRISPRs, a type of bacterial acquired immune system which is thought to be a defense against phage infection. The author’s exciting finding is that a particular kind of phage, isolated in Bangladesh from a patient suffering a V. cholera infection, encodes CRISPRs of it’s own! The phage CRISPRs target the PICI, enabling phage infection. So essentially the phage is crippling bacterial innate immunity.
Just for the cherry on top, when they knocked out the part of the phage encoded CRISPRs that targets the PICI to induce phage resistance, they got mutational escape. The phage CRISPR acquired a new PICI target, resulting in phage susceptibility showing that the phage CRISPR was functional. I would have loved to have been in the lab when they realised that!
Great work, nicely written paper, only a few pages. Give it a read.