Multiplex CRISPR/Cas9 editing of gliotoxin biosynthesis genes in Aspergillus fumigatus reduces pathogenicity in broilers.

Gliotoxin of Aspergillus fumigatus has been extensively studied for its role in pathogenesis in animals and humans. It triggers pathogenesis by its immunosuppressive and cytotoxic effects. Biosynthetic gene cluster (BGC) consisting of 13 genes regulates its biosynthesis. We targeted gliZ, gliP and gliA genes of this BGC using CRISPR/Cas9 system in a multigene editing approach to check the pathogenesis in broilers. crRNAs were designed using EuPaGDT and 3 single guide RNAs (sgRNA) were commercially synthesized. Each sgRNA was combined with Cas9 to form ribonucleoprotein complexes which were then used for simultaneously transfecting fungal protoplasts. Thin-layer chromatography showed the absence of gliotoxin on silica plate and DNA sequencing showed various indels in target genes. These indels caused amino acid substitutions in all three gene products but, the gliP mutation, since it was synonymous, was likely not functionally relevant. Regenerated protoplasts were matured to form fungal hyphae and spore production was induced. These spores were inoculated intra-air sac in broiler chicks. During one-week infection trial, birds infected with the wild-type spores (group 1) showed morbidity and their mortality rate was 30%. Birds inoculated with RNP-treated spores (group 2) showed mild clinical signs and no mortality. No morbidity or mortality was recorded in birds in negative control group (group 3). Histopathological analysis of lungs showed necrosis and congestion, and presence of mixed population of inflammatory cells in wild-type infected birds, while no such lesions were seen in birds infected with RNP-treated spores. These results show that multigene editing approach was successful in creating indels simultaneously in 3 gliotoxin genes which resulted in amino acid substitution which negatively impacted gliotoxin biosynthesis and export. In vivo experiment results show that RNP-treated fungal spores were unable to cause A. fumigatus pathogenicity in broiler. Targeting gliotoxin biosynthesis could thus be a promising approach to develop antifungal therapy.