Habitat and host related variation in sponge bacterial communities in Indonesian coral reefs and marine lakes

Marine lakes are very rare and unique global ecosystems. Isolated from the surrounding marine habitat, many now house numerous endemic species. In the present study, we compare the bacterial communities of two sponge species, Suberites diversicolor and Cinachyrella australiensis, found inside and outside the lakes. Both species housed unique bacterial assemblages, dominated by Proteobacteria and with high concentrations of Cyanobacteria (the most abundant taxon related to Synechococcus) in one of the marine lakes. Other bacterial phyla were much less prevalent or even completely absent from both species. At the class level, Alphaproteobacteria dominated the communities of Suberites whereas Gammaproteobacteria dominated communities of C. australiensis. There was no discernible difference between bacterial communities hosted by S. diversicolor inside and outside the lake. The bacterial community of this species was, furthermore, dominated by three very closely-related Alphaproteobacterial taxa that together made up 64% of all sequences. C. australiensis, in contrast, hosted markedly different bacterial communities inside and outside the lakes with very few shared abundant taxa. Dominant OTU's in C. australiensis were closely-related to taxa known to be involved in nitrogen fixation, ammonia-oxidation and sulphur-oxidation, an indication that the sponge may be an important component of nutrient cycling inside and outside of marine lakes.