CRISPR Target Location Determines the Escape Strategy of Bacteriophage | AIChE

CRISPR Target Location Determines the Escape Strategy of Bacteriophage

Authors 

Schelling, M. - Presenter, Iowa State University
Sashital, D., Iowa State University
Bacteriophages can evade CRISPR interference by developing mutations in target genomic regions. Here we challenged bacteriophage using Cas12a armed with crRNAs targeting essential and non-essential regions of the lambda phage genome. We find that phage targeted in essential genomic regions mainly develop seed region mutations. However, a mismatch in the seed region is not always sufficient to allow complete phage escape. Mutations that arise depend on the location of existing target mismatches and the sequence context in coding regions. Evidence indicates that the mutations we observe are pre-existing in the phage population at low levels. Phage targeted in non-essential genomic regions develop large deletions that remove the target and allow complete CRISPR escape. Homology at the deletion site indicates that these deletions are generated by homologous recombination, possibly after Cas effector cleavage or during phage genome replication. Our results reveal the importance of natural genetic variation in phage populations for CRISPR immunity.