Evolution and taxonomy of nematode-associated entomopathogenic bacteria of the genera Xenorhabdus and Photorhabdus: an overview

Abstract

Entomopathogenic bacteria from the genera Photorhabdus and Xenorhabdus are closely related Gram-negative bacilli from the family Enterobacteriaceae (γ-Proteobacteria). They establish obligate mutualistic associations with soil nematodes from the genera Steinernema and Heterorhabditis to facilitate insect pathogenesis. The research of these two bacterial genera is focused mainly on their unique interactions with two different animal hosts, i.e. nematodes and insects. So far, studies of the mutualistic bacteria of nematodes collected from around the world have contributed to an increase in the number of the described Xenorhabdus and Photorhabdus species. Recently, the classification system of entomopatogenic nematode microsymbionts has undergone profound revision and now 26 species of the genus Xenorhabdus and 19 species of the genus Photorhabdus have been identified. Despite their similar life style and close phylogenetic origin, Photorhabdus and Xenorhabdus bacterial species differ significantly in e.g. the nematode host range, symbiotic strategies for parasite success, and arrays of released antibiotics and insecticidal toxins. As the knowledge of the diversity of entomopathogenic nematode microsymbionts helps to enable the use thereof, assessment of the phylogenetic relationships of these astounding bacterial genera is now a major challenge for researchers. The present article summarizes the main information on the taxonomy and evolutionary history of Xenorhabdus and Photorhabdus, entomopathogenic nematode symbionts.

Nanopore-Sequencing Characterization of the Gut Microbiota of Melolontha melolontha Larvae: Contribution to Protection against Entomopathogenic Nematodes?

“…These EPN from the genera Steinernema and Heterorhabditis require intestinal mutualistic Xenorhabdus and Photorhabdus spp. bacteria (referred to as EPN bacteria) to go through their life cycle [ 20 , 21 ]. EPN infective juveniles (IJ) gain access to the insect digestive tract through natural openings, perforate the midgut wall, and release their mutualists to hemolymph.…”

Bacteria as Biocontrol Tool against Phytoparasitic Nematodes

“…These results might be caused by the upregulation of antioxidative enzyme catalase under both well-watered and drought stress conditions [94]. 2,3-butanediol (VOC) produced by Bacillus is responsible for significant improvement in plant growth [95].…”

Opportunities and challenges of entomopathogenic nematodes as biocontrol agents in their tripartite interactions

“…Xenorhabdus lacks these two features. Photorhabdus are the only light-producing bioluminescent terrestrial bacteria, but the function of this trait in Photorhabdus is still unknown (Sajnaga and Kazimierczak 2020). Both these bacteria are easy to culture in laboratory and grow fast in Luria-Bertani medium, with a doubling time of approximately 2 h. These symbiotic bacteria were isolated and classified for the first time in 1964 (Sajnaga et al 2018).…”

“…Both these bacteria are easy to culture in laboratory and grow fast in Luria-Bertani medium, with a doubling time of approximately 2 h. These symbiotic bacteria were isolated and classified for the first time in 1964 (Sajnaga et al 2018). Yet, recent advances in different aspects of these bacteria such as their evolution, taxonomy, and molecular biology with emphasis on their application to agriculture and medicine have been reviewed (Sajnaga and Kazimierczak 2020;Sajnaga et al 2018;Osimani et al 2018).…”