Environment and Diet Influence the Bacterial Microbiome of Ambigolimax valentianus, an Invasive Slug in California

SIMPLE SUMMARY: Slugs are significant pests, physically damaging plants from their voracious appetite as well as dispersing bacteria which could be harmful to plants and humans. They produce substantial economic costs, both as a direct result of plant destruction, and indirectly through attempts of pest control. This study explored the ecological aspects of the bacterial microbiome of Ambigolimax valentianus, a slug invasive to California. We identified a core microbiome in A. valentianus and found that their bacterial microbiome can be influenced and may depend substantially on both diet and environment. We also found that A. valentianus slugs harbor ecologically important bacteria, therefore their dispersal could have environmental and agricultural implications for both crop health and plant science. Future studies that provide a better understanding of the slug bacterial microbiome may be an important step in the development of comprehensive slug management. ABSTRACT: Ambigolimax valentianus is an invasive European terrestrial gastropod distributed throughout California. It is a serious pest of gardens, plant nurseries, and greenhouses. We evaluated the bacterial microbiome of whole slugs to capture a more detailed picture of bacterial diversity and composition in this host. We concentrated on the influences of diet and environment on the Ambigolimax valentianus core bacterial microbiome as a starting point for obtaining valuable information to aid in future slug microbiome studies. Ambigolimax valentianus were collected from two environments (gardens or reared from eggs in a laboratory). DNA from whole slugs were extracted and next-generation 16S rRNA gene sequencing was performed. Slug microbiomes differed between environmental sources (garden- vs. lab-reared) and were influenced by a sterile diet. Lab-reared slugs fed an unsterile diet harbored greater bacterial species than garden-reared slugs. A small core microbiome was present that was shared across all slug treatments. This is consistent with our hypothesis that a core microbiome is present and will not change due to these treatments. Findings from this study will help elucidate the impacts of slug-assisted bacterial dispersal on soils and plants, while providing valuable information about the slug microbiome for potential integrated pest research applications.