Transduction of the library reveals host genes necessary for the production of functional capsids.

(A) Overview of the experimental system to screen for λ host factors. Strain FR-E01 expressing dCas9 under aTc-inducible promoter and carrying the sgRNA library on a cosmid was infected by λ. The library can be packaged into capsids when the sgRNA does not disrupt phage propagation. After transduction into a lysogenic strain, the distribution of sgRNAs is measured by sequencing. (B) log2FC values after transduction are strongly correlated to the effect of guides on cell growth (ANOVA, F = 27263, df = 17198, p −16). (C) For each gene, a linear model was built to explain log2FoldChange after transduction while taking the effect on cell growth into account. Estimate and corrected p-value (FDR) are shown for each gene. Genes previously described as host factors are shown in red. (D) Comparison of results after infection and after transduction. Genes targeted by >1 guide which significantly decrease the production of functional phages (ANOVA, FDR nusG without infection or after infection by λ at MOI = 0.01 or MOI = 1. (F) Phage titer during infection of strain FR-E01 carrying an empty vector or expressing a sgRNA targeting nusG (MOI = 0.01). Error bars show standard deviation of three independent experiments.