United States Department of Agriculture 1 article published in JoVE Genetics Application of CRISPR Interference (CRISPRi) for Gene Silencing in Pathogenic Species of Leptospira L. G. V. Fernandes1,2, R. L. Hornsby1, A.L.T.O. Nascimento*2, J. E. Nally*1 1Infectious Bacterial Diseases Research Unit, National Animal Disease Center, Agricultural Research Service, United States Department of Agriculture, 2Laboratório de Desenvolvimento de Vacinas, Instituto Butantan Here, the application of CRISPR interference (CRISPRi) for specific gene silencing in Leptospira species is described. Leptospira cells are transformed by conjugation with plasmids expressing dCas9 (catalytically "dead" Cas9) and a single-guide RNA (sgRNA), responsible for base pairing to the desired genomic target. Methods to validate gene silencing are presented.