Infectious diseases such as white plague syndrome (WPS) and black band disease (BBD) have caused massive coral loss worldwide. We performed a metaproteomic study on the Abrolhos coral Mussismilia braziliensis in order to define the types of proteins expressed in healthy corals compared to WPS- and BBD-affected corals. A total of 6363 MS/MS spectra were identified as 361 different proteins. Healthy corals had a set of proteins that may be considered markers of holobiont homeostasis, including tubulin, histone, Rab family, ribosomal, Peridinin-chlorophyll a-binding protein, F0F1-type ATP synthase, alpha iG protein, calmodulin, and ADP-ribosylation factor. Cnidaria proteins found in healthy M. braziliensis were associated with Cnidaria-Symbiodinium endosymbiosis and included chaperones (hsp70, hsp90, and calreticulin), structural and membrane modeling proteins (actin), and proteins with functions related to intracellular vesicular traffic (Rab7 and ADP-ribosylation factor 1) and signal transduction (14-3-3 protein and calmodulin). WPS resulted in a clear shift in the predominance of proteins, from those related to aerobic nitrogen-fixing bacteria (i.e., Rhizobiales, Sphingomonadales, and Actinomycetales) in healthy corals to those produced by facultative/anaerobic sulfate-reducing bacteria (i.e., Enterobacteriales, Alteromonadales, Clostridiales, and Bacteroidetes) in WPS corals. BBD corals developed a diverse community dominated by cyanobacteria and sulfur cycle bacteria. Hsp60, hsp90, and adenosylhomocysteinase proteins were produced mainly by cyanobacteria in BBD corals, which is consistent with elevated oxidative stress in hydrogen sulfide- and cyanotoxin-rich environments. This study demonstrates the usefulness of metaproteomics for gaining better comprehension of coral metabolic status in health and disease, especially in reef systems such as the Abrolhos that are suffering from the increase in global and local threatening events.
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