CRISPRi-seq in Haemophilus influenzae reveals genome-wide and medium-specific growth determinants

Work in the human pathobiont Haemophilus influenzae has pioneered functional genomics in bacteria such as genome-wide transposon mutagenesis combined with deep sequencing. These approaches unveiled a large set of likely essential genes, but functional studies are hampered due to a limited molecular toolbox. To bridge this gap, we engineered a titratable anhydrotetracycline (aTc)-inducible CRISPRi (Clustered Regularly Interspaced Short Palindromic Repeats interference) platform for efficient regulation of gene expression in H. influenzae . Genome-wide fitness analyses in two different in vitro culture media by CRISPRi-seq revealed growth medium-dependent fitness cost for a panel of H. influenzae genes. We demonstrated that CRISPRi-programmed fitness defects can be rescuable, and refined previous Tn-seq based essentialome studies. Finally, we introduce HaemoBrowse, an extensive user-friendly online resource for visual inspection of H. influenzae genome annotations, including sgRNA spacers. The inducible CRISPRi platform described here represents a valuable tool enabling functional genomics and the study of essential genes, thereby contributing to the identification of therapeutic targets for developing drugs and vaccines against H. influenzae .