Sponge specific bacteria are wide-spread (but rare) in diverse marine habitats: Re-examining sequence data using deep-sequencing technology

Marine sponges often harbour dense and diverse microbial communities, many of these being specific to the host (Webster & Taylor, 2012).  The microbes inhabiting sponges can represent up to 40% of the volume of the sponge with representatives from fungi, Archea, bacteria and the microalgae  serving  a diverse array of functions including the production of active metabolites for defence (Schmidt et al 2000) and  energy production utilised by the host (Wilkinson, 1983). The specificity of sponge symbionts is based on 16s rRNA analysis that has shown that many of these symbionts are not present outside of the sponge, but a recent investigation using 16s rRNA gene tag pyro sequencing (advanced sequencing technology) found symbiont gene sequences in seawater (Webster et al, 2010). This discovery led Taylor et al (2012) to investigate this phenomenon further.

Through the screening of >12 million publicly available 16s rRNA gene pyrotags derived from 649 seawater, sediment, hydrothermal vent and coral reef samples 77 of the 173 previously described sponge-specific bacteria were discovered outside the host sponge. Taylor and colleagues do stress, however, that although these bacteria are present, they were extremely rare in the samples (2 seqeunce reads out of 20,000) and, as in many studies, while the gene pyrotgas may be present this does not mean the exact same organism is so widespread (an acknowledged limitation of the 16s rRNA gene as a phylogenetic marker). The Poribacter were represented in all habitats, but never exceeding 0.19% of the sample. The authors made an attempt to determine if the symbionts were active outside of the sponge through examination of RNA sequences. It is often suggested that cellular rRNA concentrations are correlated with growth rate and activity, hence rRNA may reflect which members of the community that are active (Kamke et al, 2010). Only one investigation included DNA and RNA derived samples, but analysis did suggest that symbionts may be active outside the host, but this remains unclear. Testing whether sponge symbionts can persist in differing habitats could be a relatively simple investigation, if anyone is feeling brave.  The authors allude to the purpose of these symbionts outside of the sponge highlighting the fact that vertical transmission of symbionts between generations is well documented, but do suggest that these ‘outsiders’ may act as a seed bank for sponges (Webster et al, 2010; Taylor et al, 2012).

This study highlights how the increasing resolution of new technologies is opening up avenues of investigation, and in this case, adding new players to the game. It seems unlikely that any of the previously investigated sponge specific symbionts are likely to lose their title given the minute proportions present in the samples compared to the proportions normally present in sponges. Further investigation into what role these ‘outsiders’ is required.    

REVIEWED: Taylor. W. M.,Tsai.P., Simister. R. L., Denies. P., Botte. E., Ericson.G., Schmitt. S., Webster. N. S.,(2012). ‘Sponge-specifis’ bacteria are widespread (but rare) in diverse marine environments. ISME. 1-6.

Kamke. J., Taylor. M. W., Schmitt. S., (2010). Active profile of marine sponge associated bacteria obtained by 16s rRNA vs 16s rRNA gene comparisons. ISME. 4. 498-508.

Schmidt. E. W., Obraztsova, A. Y., Davidsn. S. K.,Faulkner. D. J., Haygood. M.G.,(2000). Identification of antifungal-peptide containing symbiont of marine sponge Theonella Swinhoei as a novel delta-proteobacterium ‘Candidatus Entotheonella palauensis’. Marine Biology. 136. 969-977.

Webster. N.S., Taylor. M. W., Behnam. F., Lucker. S., Rattei. T., Whalan. S. et al, (2010). Deep sequencing reveals exceptional diversity and modes of transmission for bacterial sponge symbionts. Environmental Microbiology. 12. 2070-2082.

Webster. N. S., Taylor. M. W.,(2012). Marine sponges and their symbionts: Love and other relationships. Environmental Microbiology. 14. 335-346.

Wilkinson. C. R., (1983). Net primary productivity in coral reef sponges. Science. 219. 410-412.