Sea Urchin Larvae (Strongylocentrotus purpuratus) Select and Maintain a Unique Microbiome Compared to Environmental Sources.

AbstractMany organisms may rely on microbes that seed the host body and are typically maintained as a consortial symbiosis. Marine invertebrates have highly diverse microbiomes and offer many different life history traits across which to explore the members and functions of these symbionts but are largely absent from the holobiont and microbiome literature compared to humans and vertebrates. We tracked the microbiome of Strongylocentrotus purpuratus larvae and examined the role of vertical transmission via gametes and the role of horizontal transmission via diet and seawater for seeding the developing larvae with microbes potentially critical to holobiont health and fitness. We used 16S short-read sequencing to track the composition and relative abundances of bacteria associated with diet (microalgae) and with habitat (filtered seawater), as well as with S. purpuratus gametes and larvae under standard lab rearing conditions. The larval microbiome differed across developmental stages and between filtered seawater and algae, and specific bacterial taxa were associated with those differences. In this experiment, developing larvae selected and maintained a unique microbiome compared to their diet and habitat. Eggs were a potentially significant source of vertical transmission during embryonic development (genus Psychromonas), while horizontal transmission via filtered seawater was the main contributor to larval feeding stages, suggesting that filtered seawater is likely the most important source of potential symbionts. Gaining new insights into how marine invertebrate larval microbiomes are seeded and with what taxa is important for endangered-species aquaculture and for ecosystem restoration and management to protect inoculation sources for early-life stage organisms.