Microbiomes of the Arctic carnivorous sponges <i>Chondrocladia grandis</i> and <i>Cladorhiza oxeata</i> suggest a specific, but differential involvement of bacterial associates

Abstract

While sponges are generally known to host a wide range of microbial associates, the composition and specificity of the microbial communities in carnivorous sponges are poorly understood. We used 16S rRNA gene data to examine and compare the bacterial communities associated with distinct anatomical regions of two carnivorous sponge species, Chondrocladia grandis and Cladorhiza oxeata, sampled from Baffin Bay and the Gulf of Maine (C. grandis only). The two sponge species hosted distinct bacterial communities, with taxonomic diversity being greater in C. grandis. Some bacterial taxa (including particular oligotypes) were consistently recovered in multiple host individuals from geographically distant sites, suggesting specificity. Within C. grandis, certain bacterial taxa were enriched in particular anatomical regions, suggesting functional roles in carnivorous sponge metabolism or other biological processes. Stable isotope analysis provided no evidence for methanotrophy in the sponges examined, but Gulf of Maine C. grandis might incorporate 13 C-depleted carbon via the bacteria-mediated heterotrophic degradation of other hydrocarbons. Overall, our results demonstrate that the carnivorous sponge microbiome appears host species specific and stable, even over large geographical areas. The observed differences in bacterial community composition and diversity between C. grandis and C. oxeata may reflect differences in trophic adaptability, specialization, and overall reliance on associated bacteria.