coral disease: the invasion of cyanobacteria

Mussismilia corals can be considered as Neogene relics as one of the oldest extant clade of scleractinians, endemic to the Brazilian coast (Garcia et al., 2015), this genus of corals have had the ability to survive for at least 2.6million years, with many of the ‘cousins’ becoming extinct. The long existence of these corals indicates they have an amazing ability to adapt to its surrounds to ensure survival in times of increased stress.

The oceans are now experiencing great change with increasing temperature and carbon dioxide levels especially, we know that disease is controlled by the interactions between the host, the pathogen and probably the most prominent the environment. With such significant changes to the marine environment happening we need to be able to identify what effect is this having on the marine organism, and coral can be considered as a relatively sensitive group of marine organism.

Scientists have been increasingly studying the effect of diseases on coral, as there appears be an increase in the disease in marine systems, especially effecting corals. Garcia and team used collected samples from the Parcel dos Abrolhos reef, northeast coast of brazil, a combination of healthy, and diseased Mussismilia braziliensis, the diseased corals were either affect by black band disease(BBD) or white patch syndrome (WPS). The coral proteins were extracted using Trizol extraction, and purified with isopropyl alcohol.  Sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was performed to fractionate the proteins, and identified and given taxonomic assignments through Mascot analysis.

An interesting shift in the Metaproteome was found in this study, with a shift from healthy corals which were dominated by proteins related to Actinomycetales and plantomycetales, whereas corals with WPS where dominated by Vibro alteromanads and sulfur-reducing bacteria.  The team described a shift from proteins relating to aerobic nitrogen fixation, to facultive/anaerobic sulfate- reducing bacteria (in WPS specimens). The diverse consortium of organisms associated with coral with BBD are dominated by filamentous cyanobacteria and sulfur cycle bacteria. The bacterium associated with the diseased corals are causing a shift in functional mechanisms resulting in a healthy-to-disease transitions, although the causative agent and virulence associated with coral reef disturbances is a highly understudied aspect of coral reef biology.

This study identifies numerous different proteins which are altered, causing different functions/ pathways in the corals. Healthy corals have a proteome which represents a wide range of functions including; membrane modelling, intracellular vesicular traffic and signal transduction, as well as proteins involved in the establishment and regulation of endosymbiosis and the symbiosome. Where as many of the proteins in the Metaproteome of corals with BBD, are highly targeted towards stress response, which is very consistent with elevated oxidative stress which occurs in the microbial mat. Many of the heat-shock proteins produced in the microbial mat wee by cyanobacteria, as well as many other proteins which are related to the role of chaperonins in the stability of photosynthetic complexes and nitrogen fixation activity in the cyanobacteria.

 This study took a different approach to others in the way that it focused on the Metaproteome allowing the major metabolic pathways to be easily described. This study is breaking through in understanding coral diseases, finding how the coral holobiont is significantly altered, and changing the metabolic pathways.  

Referenced paper- Garcia, G. D., Santos, E. de O., Sousa, G. V., Zingali, R. B., Thompson, C. C., & Thompson, F. L. (2016). Metaproteomics reveals metabolic transitions between healthy and diseased stony coralMussismilia braziliensis. Molecular Ecology, 25(18), 4632–4644. doi:10.1111/mec.13775, http://onlinelibrary.wiley.com/doi/10.1111/mec.13775/pdf