Chitin contributes to the formation of a feeding structure in a predatory nematode

•Chitin contributes to teeth formation in P. pacificus •Chitin-synthase inhibitor Nikkomycin Z treatment results in teethless animals •Teethless animals can sense prey nematodes but are unsuccessful at killing Some nematode predators and parasites form teeth-like denticles that are histologically different from vertebrate teeth, but their biochemical composition remains elusive. Here, we show a role of chitin in the formation of teeth-like denticles in Pristionchus pacificus, a model system for studying predation and feeding structure plasticity. Pristionchus forms two alternative mouth morphs with one tooth or two teeth, respectively. The P. pacificus genome encodes two chitin synthases, with the highly conserved chs-2 gene being composed of 60 exons forming at least four isoforms. Generating CRISPR-Cas9-based gene knockouts, we found that Ppa-chs-2 mutations that eliminate the chitin-synthase domain are lethal. However, mutations in the C terminus result in viable but teethless worms, with severe malformation of the mouth. Similarly, treatment with the chitin-synthase inhibitor Nikkomycin Z also results in teethless animals. Teethless worms can feed on various bacterial food sources but are incapable of predation. High-resolution transcriptomics revealed that Ppa-chs-2 expression is controlled by the sulfatase-encoding developmental switch Ppa-eud-1. This study indicates a key role of chitin in the formation of teeth-like denticles and the complex feeding apparatus in nematodes. Some nematode predators and parasites form teeth-like denticles that are histologically different from vertebrate teeth, but their biochemical composition remains elusive. Here, we show a role of chitin in the formation of teeth-like denticles in Pristionchus pacificus, a model system for studying predation and feeding structure plasticity. Pristionchus forms two alternative mouth morphs with one tooth or two teeth, respectively. The P. pacificus genome encodes two chitin synthases, with the highly conserved chs-2 gene being composed of 60 exons forming at least four isoforms. Generating CRISPR-Cas9-based gene knockouts, we found that Ppa-chs-2 mutations that eliminate the chitin-synthase domain are lethal. However, mutations in the C terminus result in viable but teethless worms, with severe malformation of the mouth. Similarly, treatment with the chitin-synthase inhibitor Nikkomycin Z also results in teethless animals. Teethless worms can feed on various bacterial food sources but are incapable of predation. High-resolution transcriptomics revealed that Ppa-chs-2 expression is controlled by the sulfatase-encoding developmental switch Ppa-eud-1. This study indicates a key role of chitin in the formation of teeth-like denticles and the complex feeding apparatus in nematodes.