Scratching the surface of coral related bacteria.

Coral reefs are extremely diverse ecosystems, the most diverse in the marine environment. However, the majority of this diversity is still uncharacterised. Biodiversity analyses have been carried out on eukaryotes, in a couple of ways, whereas the unicellular members have been very much ignored even though they’re the most diverse group on the planet (Rohwer et al., 2002)

In this study by Rohwer et al., (2002), 3 coral species were analysed for uncultured unicellular diversity, attempting to address characterisation of these unicellular bacteria.

Three coral species were analysed for uncultured unicellular diversity.  The coral species used were Montastraea franksi, Diploria strigosa and Porites asteroides. These were collected from two separate locations in the Western Atlantic, being Panama and Bermuda. They used a punch and hammer to remove 1.3cm diameter cores from the upper surfaces of the three coral species, 5 M.franksi, 4 D.strigosa and 5 P.asteroides. The samples were always taken at least 10 metres apart except for one cluster sample, in order to assess differences in proximities. All corals were disease free at the time of collection. The DNA was then amplified, sequenced and analysed (Rohwer et al).

The 14 samples of coral contained a total of 430 bacterial ribotypes, with most sequences being observed in 10 clones or less. However, using the Chao 2 estimator (Chao 1984), the combined libraries may have contained up to a total of 6000 different distinct ribotypes. The samples collected from Panama possessed a far greater number of ribotypes than those collected from Bermuda. The most common groups found were gamma proteobacteria (38%), alpha proteobacteria (17%), Bacillus/Clostridium (13%),  Cytophaga-Flavobacter/Flexibacter bacteroides (13%) and cyanobacteria (6%), with 14% being unidentifiable. However, these abundances varied substantially between samples. Some bacterian groups were much more common in particular species than in others (Rohwer et al).

It is known that metazoan biodiversity on coral reefs is extremely high. Results from this study by Rohwer et al (2002)., suggest that this is also the case in the bacteria associated with coral reefs. They also infer that the majority of these species are novel to the genus and species level. This is shown by half of the sequences sharing less than 93% identity to previously published 16S sequences.

Rohwer et al., 2002, also present evidence that the bacteria maintain species-specific associations to certain coral species. Although, they find very different bacteria associated with D.strigosa when compared to a study by Frias Lopez et al., 2002.

I believe this paper is only scratching the surface on bacteria associated with coral reefs. Considering they only sampled three species of coral from two sites, yet found up to 6000 distinct ribotypes shows the potential abundance of these bacteria. Rohwer et al., (2002), suggest that the role of these bacteria may be nitrogen fixation, or possibly antibiotic producers etc. Once the different types of bacteria associated with corals has been distinguished, I think that then it would be very interesting to look at their potential roles, pros and cons for the corals etc. I hope to address this topic further in a more recent paper in my next post.    

Chao A (1984). Non-parametric estimation of the number of classes in a population. Scandinavian Journal Statistical 11, 783–791.

Rowher, F., Seguritan, V., Azam, F., Knowlton, N. (2002). Diversity and distribution of coral-associated bacteria. Marine Ecology Process Series, 243, 1-10.

Frias-Lopez J, Zerkle AL, Bonheyo GT, Fouke BW. (2002) Partitioning of bacterial communities between seawater and healthy, black band diseased, and dead coral surfaces. Applied and Environmental Microbiology, 68, 2214–2228