The ecology of marine sponge-associated microorganisms
 Many marine sponges contain dense, highly diverse microbial communities. More than 10 bacterial phyla (including Proteobacteria, Actinobacteria, Nitrospira, Chloroflexi, Planctomycetes, Cyanobacteria, Acidobacteria) have been found in sponges, as well as both major lineages of Archaea and a range of unicellular eukaryotes such as diatoms and dinoflagellates. Collectively, these organisms exhibit an enormous diversity of metabolic traits of potential use to the host, including nitrification, photosynthesis, anaerobic metabolism and secondary metabolite production. However, in most cases the exact nature of the interactions between sponges and microbes remains a mystery, and to an individual sponge a given microorganism could represent a potential food source, a pathogen, a parasite or a symbiont.
 Marine sponges - and the microbes living within them - are important from both an ecological and a biotechnological viewpoint. Sponges are important members of shallow and deep water reef communities, with nutrition supplied by photosynthetic symbionts often allowing them to compete with other benthic organisms such as corals. Sponges are also renowned as a rich source of biologically active metabolites, many of which have antimicrobial, antiviral or antitumor properties. In at least some cases these metabolites are produced by the microbes, rather than the sponge itself. Sponges and their associated microorganisms are therefore receiving much attention from pharmaceutical companies.
Advances in molecular techniques over the past two decades have greatly contributed to our knowledge of microbial diversity in sponges. Clone libraries based on the 16S ribosomal RNA (16S rRNA) gene have revealed unexpected diversity (including the novel, seemingly sponge-specific candidate phylum 'Poribacteria';  Fieseler et al. 2004 [PDF]), while fluorescence in situ hybridisation has provided quantitative information on the abundance of various phylogenetic groups within sponge tissue. The continued development and application of such methods will further our understanding of the diversity and, ultimately, function of sponge-associated microorganisms. In our department we aim not only to increase our knowledge of the identity of putative symbionts but, importantly, to relate this information to the biology of both the microbes and the host sponges.
Investigated by: Michael Wagner, Faris Behnam
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