The Body Wall Microbiome of the Terrestrial Slug Deroceras laeve Reveals Potential Endosymbionts and Shares Core Organisms with Other Mollusks.

The marsh slug Deroceras laeve is an invasive mollusk found in gardens, field crops, and wetlands. It lacks a protective shell, suggesting that microbial communities are associated with its adaptability to the environment. Here, we used a whole shotgun metagenomic approach to analyse the complex microbiome of D. laeve and compared it to that of other mollusks. This demonstrated the presence in D. laeve of bacteriophages such as Erwinia phage, Certrevirus, and Machinavirus, which target plant pathogen bacteria. In the Archaea domain the halophilics Halovivax and Halobaculum predominated, but also present were the methanogens Methanobacterium, Methanobrevibacter, Methanocaldococcus, Methanococcus, and Methanosarcina, involved in phosphate solubilization and methanogenesis during decomposition of organic matter. The Bacteria domain was dominated by γ-Pseudomonadota such as Buttiauxella, Citrobacter, Enterobacter, Klebsiella, Kluyvera, Leclercia, and Pseudomonas which are producers of enzymes that degrade biomass and complex carbohydrates. Regarding the fungal community, filamentous or yeast ascomycetes predominated such as Debaryomyces, Puccina, and Pyricularia known as plant pathogens or associated with decaying organic matter. Consistent with these findings, functional analysis revealed enrichment in genes involved in fermentation and carbohydrate metabolism. Remarkably, regardless of species, ecosystem, and tissue type, we found that the core microbiome of the mollusks in this study is mainly structured by the Phyla Uroviricota, Euryarchaeaota, Pseudomonadota, and Ascomycota, with diversity at the genus level. This suggests ancient symbiotic interactions of these mollusks with specific types of microbes which may have been critical for adaptability to their environment.