Dimethylsulfoniopropionate (DMSP) is a highly, hugely, massively important substance in nature. DMSP is produced by algae and plants as an osmoregulator; these organisms release copious amounts DMSP into the environment where it is metabolized into dimethyl sulfide (DMS) by a handful of microbial species. DMS is responsible for that sulfurous, fishy “ocean smell” that we may encounter either while visiting the beach or while digging around in an aquarium.
Incidentally, DMS plays a huge role in climate, as it serves to condense water vapor, which promotes cloud formation. So, think about the big picture here… Algae/plants release lots of DMSP as they grow, which ultimately contributes to cloud cover, which limits the amount of sunlight that reaches the Earth’s surface, which limits algae/plant productivity. It’s a marvelous self-regulating process that has modulated all of our planet’s biomes for eons.
Shallow-water coral reefs are known to generate substantial quantities of DMSP. This is due primarily to the activity of coral-associated dinoflagellates (i.e. zooxanthellae). Though it technically is a waste product, DMSP does appear to benefit the coral host when present in small amounts. For example, it helps to mitigate intracellular oxidative stress. However, as it builds up, it becomes a liability. Why? The über coral pathogen Vibrio (V. harveyi, V. coralliilyticus, etc.) uses DMSP (though not DMS) as an infochemical to locate physiologically stressed corals. Vibrio cannot metabolize DMSP (despite its rich carbon and sulfur content); apparently, the substance serves this pathogen solely as a chemical cue in its search for weakened hosts.
As we all know, zooxanthellate corals experience all kinds of stressors while in captivity. Heat stress during the summer months… Light stress during photoacclimation… Many of these events lead to elevated DMSP levels. The last thing we want when our prized corals are stressed out is to invite Vibrio to attack them. Vibriotic infection is implicated in (among other things) the rapid necrosis of coral tissue, a condition that aquarium hobbyists describe aptly as Rapid Tissue Necrosis (RTN).
Sometimes RTN occurs in relatively isolated infections, affecting a small number of related stony corals; sometimes it can be devastating, wiping out entire collections. The latter case is especially destructive and costly where susceptible coral species are more or less monocultured at high density (e.g. coral farms). Regardless, the high attrition of this disease, and the apparent difficulty of treating it, make any means of prevention look quite attractive.
The good news is that certain ecologically important DMSP-consuming microbes have been isolated from healthy corals and identified (Endozoicomonas acroporae, Roseobacter denitrificans, etc.). The bad news is that while at least some of these microbes are amenable to culture, few or none of them have yet been cultivated at a commercial scale for reef aquarium use.
So we end this piece on neither a good note nor a bad one, but rather a hopeful one. While the aquarium industry generally trails behind the scientific community when it comes to reef microbiology, there may indeed come a time when aquarium hobbyists (1) comprehend the role of DMSP in coral pathology and (2) have the means to introduce target microorganisms for the purpose of preventing DMSP accumulation. Used alongside certain anti-vibriotic bacteria (e.g. Rhodopseudomonas), they may present a natural, safe and reliable line of defense against RTN. Given the increasing interest in aquarium microbiology as well as the increasing capabilities of aquarium microbiologists, the availability of such products may be all but inevitable.
For more information on this subject, check out the links below.
