Cas9-mediated gene disruption in tetraploid Giardia intestinalis

CRISPR/Cas9 system is an extremely powerful technique that is extensively used for various genome modifications in different organisms including parasitic protists. Giardia intestinalis , a protist parasite infecting about 280 million people around the world each year, has been eluding the routine use of CRISPR/Cas9 for generating knock-out cell lines due to the presence of four copies of each gene in its two nuclei. Apart from single exception employing rather laborious Cre/loxP system, no full knock-out cell line has been established yet. In this work, we show the ability of in-vitro assembled CRISPR/Cas9 components to successfully edit the genome of G. intestinalis . We further established a cell line stably expressing Cas9 in both G. intestinalis nuclei. Subsequent introduction of a template for homologous recombination containing the transcription units for the resistance marker and gRNA resulted in the removal of all gene copies at once for three independent experimental genes, mem, cwp1 and mlf1 . The method was also applicable for the incomplete disruption of an essential gene, as documented by markedly decreased expression of tom40 . Finally, testing the efficiency of Cas9-induced recombination revealed that homologous arms as short as 150 bp can be sufficient to establish a full knock-out cell line in G. intestinalis . ### Competing Interest Statement The authors have declared no competing interest.