The juvenile Antarctic whelk Neobuccinum eatoni maintains a specialized microbiome in its proboscis even in adulthood

Abstract Microbiomes are crucial for the health, physiology, and environmental adaptation of marine multicellular organisms. In Antarctica, marine invertebrates have developed unique physiological functions and adaptive strategies to withstand extremely cold and unstable conditions. However, diversity and role of the microbiome of Antarctic mollusks remains largely unexplored. In the present study, we investigated the diversity, and the putative functional role of the microbiome of the proboscis of the whelk Neobuccinum eatoni , one of the endemic species that dominate the Antarctic benthic ecosystems. We compared the microbiomes of both juveniles and adults and female and male specimens to understand potential changes across different life stages and the sex of the host. In addition, we investigated the microbiome of N. eatoni ’s habitat to explore possible transmission pathways between host and environment. Results showed the presence of a microbiome core shared among all the individuals of N. eatoni, which remained stable across different life stages and sexes, accounting, on average, for up to 91% of the total microbiome. The core was mostly represented by bacterial members belonging to the genera Sulfurospirillum , Mycoplasma , and Polaribacter . These bacteria are characterized by putative metabolic functions specialized in chemoheterotrophy and the reduction of sulfur compounds, thus supporting N. eatoni in the degradation/digestion processes of even the most refractory food sources. In addition, the absence of these bacteria in the sediments of the surrounding environment suggests a vertical transmission of the microbiome through the whelk generations. These findings expand knowledge of the diversity and key role of the microbiome in Antarctic invertebrates providing insights into the microbiome contribution to holobiont survival to polar environments.