Abstract:
CRISPR-Cas is a prokaryotic adaptive immune system that recognizes and degrades specific nucleic acid invaders, producing a “memory” of past infections that allows for heritable immunity. CRISPR-Cas systems are widespread among prokaryotes, including many human pathogens such as Staphylococcus aureus and S. epidermidis. These species can cause severe diseases, increasingly so with rising proportions of antibiotic-resistant staphylococcal infections being reported, including the ‘superbug’ MRSA. Novel therapies are required to deal with the growing antibiotic resistance crisis and prevent a post-antibiotic era. These therapies may include using novel bactericidal agents, such as bacteriophages, as well as strategies to combat the transfer of antibiotic resistance between these pathogens. CRISPR-Cas stands poised as a major potential barrier to the implementation of bacteriophage therapy, as these systems can adapt and make whole populations of bacteria immune to these treatments. Additionally, CRISPR-Cas is known to block horizontal gene transfer of antibiotic resistance plasmids between staphylococcal strains, and is thus crucial for limiting the spread of antibiotic resistance. Understanding how this system functions will aid the development of novel ways to modulate these systems to allow for successful bacteriophage therapies and prevent the spread of antibiotic resistance. We have investigated the mechanistic roles of the cas genes in S. epidermidis CRISPR-Cas immunity and identified non-Cas nucleases that may also be involved in this immunity, linking CRISPR to important physiological processes such as RNA degradation and recycling. Additionally, we have started characterizing transcriptional regulation of CRISPR-Cas in this important human pathogen, identifying environmental cues that the bacteria use to ‘decide’ when to permit or deny entrance of nucleic acid invaders. Finally, we are beginning to probe the ways in which bacteriophages suppress the bacterial immune response to permit infection in the face of CRISPR immunity.
