Microbes from all domains are involved in associations with sponges. The microbial communities of the Porifera have been uncovered by recent technological advances as being highly diverse. Transmission electron microscopy, fluorescence in situ hybridization, polymerase chain reactions and pyrosequencing advances have all made their contributions to our current knowledge of sponge microbiota, from across a range of habitats and Porifera species. Strong host selection of certain microbial groups has been indicated by similarities between sponge-associated taxa which are geographically and phylogenetically disparate.
Pyrosequencing innovations have recently uncovered new findings about these inhabitants of sponges, providing sequence data which is able to detail the less easily detectable microbes and dynamics of their communities.
Of the few studies that have paid attention to the archaeal members of sponge microbiota, there is a suggestion that Archaea can be large portions of such communities. Given that Archaea are known to be potent nitrogen cyclers, they should be heeded when considering sponge biology.
This study pyrosequenced the 16S rRNA genes isolated from 2 Inflatella pellicula sponges collected at 2900 m. The sample size is very small, but justifiable given the costs of sampling organisms from such extreme depths. Nonetheless, the data is indeed an intriguing initial insight into deep sea sponge microbiota.
The presence of archaeal sequences dwarfed bacterial ones in both sponge 1 (IpA) and sponge 2 (IpB), comprising 61 % and 73.5 % respectively. In contrast, only 11.3 % of seawater sequences were archaeal. Sponge-associated Archaea were almost exclusively of the Cenarchaceae family in the phyla Thaumarchaeota, which represented half of seawater derived archaeal sequences. Just one operational taxonomic unit (OTU) utterly dominated both sponges, yet was barely present in seawater. Previous reports of archaeal relative abundances in sponges have been modest, ranging from 4 to 28 % and consisted mostly of the archaeal phylum Crenarchaeota.
PCR amplifications of archaeal amoA genes isolated from sponge tissue have recently indicated an ammonia-oxidation role of Archaea in sponge symbioses. The dominance of a single archaeal group in sponge tissues supports this idea, as it suggests host selection of a particular symbiont. The dominant OTU had high similarity to Cenarchaeum symbiosum, an Archaea which possesses genes expected to be for ammonia oxidation and nitrogen cycling. Metatranscriptomics in another sponge species has shown abundant transcripts of ammonia oxidation genes.
Unlike the Archaea, bacterial phyla were less numerous in the sponges than in the seawater and only 4 bacterial phyla were unique to sponge communities. There were however 10 phyla found exclusively in seawater. Sequences related to Proteobacteria and Planctomycetes dominated sponge-associated Bacteria, but were scarce in seawater. A single OTU was 99 % of the beta-proteobacterial sequences collected; previously it was only associated with corals and appears to be characteristic of coral and sponge symbionts. Some of the bacteria isolated are speculated to represent new phyla with ammonia oxidising capabilities.
This is an excellent example of how new microbiological techniques can allow us to suddenly observe previously invisible phenomena. Massively parallel sequencing techniques could reveal the archaea to be much more prevalent and important than previously thought. I am curious to see if increasing depth corresponds to a shift from bacterial to archaeal dominance in symbiotic associations. These findings offer excellent reasons to investigate further into the symbioses of archaea, which seems to be a largely ignored domain of life.
Jackson, S. A., Flemer, B., McCann, A., Kennedy, J., Morrissey, J. P., O’Gara, F., & Dobson, A. D. (2013). Archaea Appear to Dominate the Microbiome of Inflatella pellicula Deep Sea Sponges. PloS one, 8(12), e84438.