Genome-wide CRISPR-dCas9 screens in E. coli identify essential genes and phage host factors

High-throughput genetic screens are powerful methods to identify genes linked to a given phenotype. The catalytic null mutant of the Cas9 RNA-guided nuclease (dCas9) can be conveniently used to silence genes of interest in a method also known as CRISPRi. Here, we report a genome-wide CRISPR-dCas9 screen using a pool of ~ 92,000 sgRNAs which target random positions in the chromosome of E. coli . We first investigate the utility of this method for the prediction of essential genes and various unusual features in the genome of E. coli . We then apply the screen to discover E. coli genes required by phages λ, T4 and 186 to kill their host. In particular, we show that colanic acid capsule is a barrier to all three phages. Finally, cloning the library on a plasmid that can be packaged by λ enables to identify genes required for the formation of functional λ capsids. This study demonstrates the usefulness and convenience of pooled genome-wide CRISPR-dCas9 screens in bacteria in order to identify genes linked to a given phenotype.