AUTHOR=Sheehy Laura , Cutler James , Weedall Gareth D. , Rae Robbie 

TITLE=Microbiome Analysis of Malacopathogenic Nematodes Suggests No Evidence of a Single Bacterial Symbiont Responsible for Gastropod Mortality

JOURNAL=Frontiers in Immunology

VOLUME=13

YEAR=2022

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2022.878783

DOI=10.3389/fimmu.2022.878783

ISSN=1664-3224

ABSTRACT=<p>Nematodes and bacteria are prevalent in soil ecosystems, and some have evolved symbiotic relationships. In some cases, symbionts carry out highly specialized functions: a prime example being entomopathogenic nematodes (EPNs), which vector bacteria (<italic>Xenorhabdus</italic> or <italic>Photorhabdus</italic>) into insect hosts, killing them to provide a food source for the nematodes. It is thought that the commercially available malacopathogenic (kills slugs and snails) biocontrol nematode <italic>Phasmarhabditis hermaphrodita</italic> vectors a bacterium (<italic>Moraxella osloensis</italic>) into slugs to kill them. To investigate this further we used a metagenomic approach to profile the bacteria present in the commercial strain of <italic>P. hermaphrodita</italic>, a wild strain of <italic>P. hermaphrodita</italic> and two other <italic>Phasmarhabditis</italic> species (<italic>P. californica</italic> and <italic>P. neopapillosa</italic>), after they had killed their slug host (<italic>Deroceras invadens</italic>). We show that these nematodes do not exclusively associate with one bacterium but a range of species, with members of the phyla Pseudomonadota, Bacillota, Actinobacteriota and Bacteroidota the most prevalent. The commercial strain of <italic>P. hermaphrodita</italic> had the least diverse bacterial community. Furthermore, we found that the bacterium <italic>P. hermaphrodita</italic> has been cultured on for 25 years is not the expected species <italic>M. osloensis</italic> but is <italic>Psychrobacter</italic> spp. and the only strain of the <italic>Phasmarhabditis</italic> species to associate with <italic>Psychrobacter</italic> spp. was the commercial strain of <italic>P. hermaphrodita</italic>. In summary, we found no evidence to show that <italic>P. hermaphrodita</italic> rely exclusively on one bacterium to cause host mortality but found variable and diverse bacterial communities associated with these nematodes in their slug hosts.</p>