Bacterial Community Composition and Functional Potential of the Kleptoplastic Sea Slug Elysia papillosa

Certain sacoglossan sea slugs, often known as "solar-powered sea slugs", are a group of marine gastropods that have the unique ability to photosynthesize by stealing functional chloroplasts from algae. The sacoglossan Elysia papillosa can maintain functional chloroplasts for up to two weeks after feeding. The microbiome of these slugs may play a crucial role in their metabolism, immunity, development, but more importantly their photosynthesis. Shotgun metagenomic sequencing was conducted on four samples of E. papillosa in order to characterize their microbiome. Sequences were classified and relative abundance was quantified with Centrifuger and functional data was examined using SqueezeMeta. Bacteria were analyzed by taxonomic groups and hypothesized function to the sea slug was determined with literature analysis. All samples were dominated by phyla Actinomycetota, Bacillota, Patescibacteriota, and Pseudomonadota. The presence of the phyla Bacteroidota and Bacillota was notable in all samples, which contain species known to produce enzymes that break down polysaccharides. It is possible that these bacteria could assist in degradation of the polysaccharide xylan found in the cell walls of Penicillus, the algal food source of E. papillosa. One species that was found in all samples was Cutibacterium acnes which has been shown to be an important component of the gut microbiota in other marine invertebrates and may provide the host with vitamin B12 and other beneficial nutrients. Many of these bacteria may be opportunistic rather than commensal. As a result, more research is required to describe the interactions between the slug and its microbiome, but this preliminary report provides a valuable starting point for identifying the microbiome make-up to further understanding of these relationships.