Determination and Ecological Impacts of the Microbiota of Moon Snail Egg Collars

Abstract

Moon snails are predatory marine snails with estimates of over 250 species found worldwide. Many studies on these snails have focused on species identification and their ecological impacts, specifically on clam populations. When moon snails lay their egg masses, they use sand and mucus to solidify the structure in a "collar" shape. Field and literature observations suggest that these collars do not experience infections despite being a rich source of nutrients and their texture changes from "firm" to "fragile" as they age. We hypothesize that the egg collars are chemically protected by associated symbiotic relationships with bacterial communities as this is common among marine animals. These communities aid in digestion, nutrient acquisition, and protection. Here, we investigated the identity and ecological impact of the microbial community associated with egg collars belonging to the moon snail Neverita delessertiana. In Chapter 2, 16S rRNA sequencing revealed the collars contain a microbiota distinct from the surrounding sediment that is dominated by members of the Flavobacteriaceae. Alpha-diversity analysis indicated the collars were selecting for/against specific bacterial strains. Using this information, Chapter 3 focuses on binary competition assays between Flavobacteriaceae, where strains isolated from egg collars identified eight strains that inhibited growth. Chemical analysis of one strain, Cellulophaga omnivescoria EM610 led to the identification of the known antibacterials bacillimidazoles A and E. Previous studies suggested these compounds were formed spontaneously, and we expanded this understanding to include additional compounds and kinetic studies. Although they are produced spontaneously, these compounds are ecologically relevant as bacillimidazole A was detected on in 62% of egg collar extracts. Finally, in Chapter 4, analysis of the carbohydrates present in egg collar mucus revealed the presence of unusual sugars in the O-glycans (e.g., xylose and glucuronic acid) and uncommon modifications on the N-glycans (e.g., methylations). Analysis of metagenomic assembled genomes identified over 2,000 glycoside hydrolases, many of which are able to cleave the glycan bonds identified in the collar mucus. These results suggest that Flavobacteriaceae play an ecological role by protecting and degrading the moon snail egg collars. This work paves the way for future investigations into the ecological impact of moon snails beyond their predation habits, highlighting the importance of marine animal-microbe symbiotic systems.