Symbiotic prokaryotic communities in sponges
Nitrogen is an essential and limiting nutrient in tropical waters and sponges provide a unique environment in which the biogeochemical cycling of nitrogen can take place. Nitrification in particular, occurs in a variety of sponges and can contribute a significant amount of dissolved inorganic nitrogen (DIN) to the surrounding coral reef environment. Xestospongia muta is ecologically important and numerically dominant component of Caribbean coral reefs. Field studies on DIN fluxes of X. muta from coral reefs around the Caribbean revealed a large variation in the flux of DIN among individual sponges and locations with the result that that this species of sponge can act as both a source and sink for DIN. Targeted studies of marker genes for nitrogen fixation and ammonia oxidation were conducted and showed the presence of both of these genes in the prokaryotic community of X. muta. Additionally, an investigation of the prokaryotic community associated with X. muta, compared with the surrounding water column, using a metagenetic approach with 454 pyrosequencing and the 16S rRNA gene yielded a quantitative picture into the composition of the symbiotic prokaryotic community. This analysis included the identification of prokaryotes that can potentially perform denitrification, and others that may be involved in sulfur cycling. These results have implications for better understanding the functional role that symbiotic prokaryotes have in the biology of the host sponge and the ecology of the reefs they are found on through their role in processes such as nutrient biogeochemistry. |  |  | |