ARBS - A Polymicrobial Puzzle?

Both corals and Sponges possess vibrant microbial communities and so are both of interest to microbiologists. Unfortunately sponges also share another similarity with corals, reports of diseases in sponges are increasing. One particular disease is Aplysina red band syndrome or ARBS, which affects Aplysina cauliformis in the Caribbean. The disease is not lethal but does cause necrosis, lesions teaming with cyanobacteria, reduced growth and physiological and biochemical changes to the sponge.  But very little is known about what causes this affliction. or how the sponge’s microbiota responds. Olson et al. (2014) collected branches of visibly healthy and ARBS affected sponges from two sites using SCUBA, in Belize and the Bahamas. Samples were frozen, DNA extracted and clone libraries created by amplification of bacterial 16S rRNA. They also carried out a technique called terminal restriction fragment length polymorphism (TFLP), which allowed them to roughly enumerate the abundance of certain sequences and so bacteria (or groups of). They also cultured the cyanobacterium Leptolyngbya, which they thought may be a cause of the disease due to its presence in lesions and its bright red colour, which they used to infect healthy sponges in the field.

Generally they discovered that although there was a fairly large dissimilarity between the healthy and ARBS-affected sponge microbiota, a core community is maintained across both health states dominated by Chloroflexi and Proteobacteri, with high variation between location and collection year in community. Overall eight bacterial phyla were found, with their relative proportion varying on disease status. In terms of bacteria that were found to increase a sequence, Leptolyngbya spp. (and Phormidium) was found to increase along with two sequences of Gammaproteobacteria. Overall the photosynthetic symbiont Symbiodinium spongiarum declined, along with four (possibly) sponge related Gammaproteobacteria and a decrease in the group Chloroflexi. However in results of the transmission experiment showed that Leptolyngbya cannot cause the disease in healthy coral on its own. So what does? Unfortunately the study could shed little light on this, but it does suggest that the pathogen could be opportunistic, viral or eukaryote (not detected by 16S rRNA), or the disease may have an archaeal component which may not have been assayed effectively if the primers used did not target this group. Another possibility is that the infection has a polymicrobial basis and given the similarities to coral black-band disease (another polymicrobial infection), this strikes me as plausible. For example, cyanobacteria of the Leptolyngbya genus are present in black band that is also characterised by large communities of cyanobacteria at infection sites. In fact a red band disease does occur in corals in a similar way to black band (Munn 2011). So it might be fruitful to take some of the lessons learned from black band disease research and apply them to this problem. Either way, sponge diseases need to be studied to a greater degree than they currently are. We require much more intensive study on the ailments of this phyla especially in light of the decline of corals and the increasing role which sponges are likely to play due to this in future tropical ecosystems.

Munn, C.B. (2011). Marine Microbiology: Ecology and Applications, 2^nd ed. New York: Garland Science.

Olson, J.B., Thacker, R.W. and Gochfeld D.J. (2014). Molecular community profiling reveals impacts of time, space, and disease status on the bacterial community associated with the Caribbean sponge Aplysina cauliformis. FEMS Microbial Ecology, 87, 268-279.