A CRISPRi-based genetic resource to study essential Staphylococcus aureus genes

We have optimized a CRISPR interference system to facilitate gene knockdown in the gram-positive bacterial pathogen Staphylococcus aureus. Our approach used a CRISPRi system derived from Streptococcus pyogenes, which involves the co-expression of the dcas9 gene encoding a catalytically inactive Cas9 protein and a customizable single guide RNA (sgRNA). In our system, dcas9 is expressed from a single copy in the chromosome of methicillin resistant S. aureus (MRSA) strains COL or JE2, under the control of a tightly regulated promoter, inducible by anhydrotetracycline. The sgRNAs are expressed from a replicative plasmid under the control of a constitutively active promoter. This system enables efficient, inducible, knockdown of both essential and non-essential genes. Using this approach, we constructed the Lisbon CRISPRi Mutant Library (LCML) comprising 261 strains, in the JE2 background, containing sgRNAs targeting 200 essential genes/operons. This library facilitates the study of the function of essential S. aureus genes and is complementary to the Nebraska Transposon Mutant Library which consists of nearly 2000 strains, each carrying a transposon insertion within a non-essential gene. The availability of these two libraries will facilitate the study of S. aureus pathogenesis and biology. Abstract ImportanceStaphylococcus aureus is an important clinical pathogen that causes a high number of antibiotic resistant infections. The study of S. aureus biology, and particularly of the function of essential proteins, is of particular importance to develop new approaches to combat this pathogen. We have optimized a CRISPRi system that allows efficient targeting of essential S. aureus genes. Furthermore, we have used that system to construct a library of 261 strains which allow the depletion of essential proteins encoded in 200 genes/operons. This library, which we have named Lisbon CRISPRi Mutant Library (LCML), should facilitate the study of S. aureus pathogenesis and biology.