The genome of a steinernematid-associated bacterium encodes the biosynthesis of insect toxins.

Several species of soil-dwelling nematodes are used in the biocontrol of crop pests, due to their natural capacity to kill diverse lepidopteran species. Although this insect-killing trait is known to be augmented by the nematodes' endosymbionts, the role of other steinernematid-associated bacterial genera in the nematode lifecycle remains unclear. This genomic study aimed to determine the potential of to contribute to the entomopathogenicity of its host. Insect larvae were infected with three separate cultures. From each of the three treatments, the prevalent bacteria in the haemocoel of cadavers, four days post-infection, were isolated. These three bacterial isolates were morphologically characterised. DNA was extracted from each of the three bacterial isolates and used for long-read genome sequencing and assembly. Assemblies were used to delineate species and identify genes that encode insect toxins, antimicrobials, and confer antibiotic resistance. We assembled three complete genomes. Through digital DNA-DNA hybridisation analyses, we ascertained that the haemocoels of insect cadavers previously infected with sp. Kalro, sp. 75, and sp. 97 were dominated by Kalro, 75, and 97, respectively. Kalro and 97 formed a subspecies with other symbionts of steinernematids from Kenya. 75 phylogenetically clustered with pseudomonads that are characterised by high insecticidal activity. The 75 genome encoded the production pathway of insect toxins such as orfamides and rhizoxins, antifungals such as pyrrolnitrin and pyoluteorin, and the broad-spectrum antimicrobial 2,4-diacetylphloroglucinol. The 75 genome encoded resistance to over ten classes of antibiotics, including cationic lipopeptides. Steinernematid-associated bacteria hence have the biosynthetic potential to contribute to nematode entomopathogenicity.