No activity on this thread for a while. There were several questions raised that I think were actually answered in one of the papers that were mentioned. I read through the "Biosysnthesis of 'essential' amino acids by
scleractinian corals" - Fitzgerald and Szmant in Biochem, J, 1997,
322, 213-221.
In that study they fed corals either radio-labelled glucose, or the radio-labelled amino acids glutamic acid, lysine, or valine. They did the proper controls (IMO) to ensure that contaminating bacteria were not affecting their results. The feeding was done by simply putting the corals in filtered seawater with the various nutrients in the water.
First of all, clearly they had consumption of the amino acids, and the glucose from the water by the coral, and incorporation of the 14C labelled atoms into amino acids and other cellular constituents (proteins, etc.). They used several different species of coral as test subjects, including both photosynthetic, and non-photosynthetic corals, including one Acropora species.
SO, corals CAN take up amino acids (at least 3), and glucose direct from the water. It doesn't seem likely to me that there is much glucose floating around in seawater, too easily consumed a nutrient source. Corals CAN however receive sugars (such as glucose I would assume) direct from their zooxanthellae. The purpose of the study these folks performed however, was to try and figure out which amino acids were 'essential' to corals.
Essential amino acids are defined as those which a particular organism can not synthesize itself from simpler molecules. Apparently no one had previously done this work on corals. In humans we know that 10 amino acids are 'essential'.
These researchers showed that starting with glucose, corals can synthesize at least 16 amino acids, possibly 19, but they could not measure 3 of them. But corals cannot synthesize the amino acid threonine.
The researchers also showed that starting with the amino acid glutamic acid the corals could synthesize at least 14 other amino acids (though 5 were low enough to be considered questionable). From the amino acid lysine or valine corals could make the same set of amino acids as with glutamic acid.
In this study, the scientists were able to isolate the metabolism of the zooxanthellae, from that of the coral tissue itself. It is known (apparently) that zooxanthellae can on their own synthesize all of the 20 normally occuring amino acids. It is also known (referred to other papers) that "only a few non-essential amino acids such as alanine and glutamate are excreted from zooxanthellae". So...the algae living in the corals tissues are not exactly nice about handing over amino acids they make to the coral itself.
What does it all mean for us? We who want to grow corals fast that have pretty colors..
..I'm not really sure. It is one interesting fact that the one amino acid they are sure corals cannot make is threonine. Since
corals can make at least 16, and perhaps all 19 other amino acids, they would not likely be 'starved' for most amino acids if they did not receive them from the water column in some form, either as food, or by direct absorption. Still it is QUITE possible that corals might grow faster?, or be more colorful? if they had additional access to some amino acids direct from the water column.
In the FWIW category the amino acids that are formed to the 'least' extent by corals are the same ones that are considered 'essential' for many other organisms: tyrosine, valine, methionine, leucine, isoleucine, phenylalanine, histidine, lysine, and tryptophan. Whether there would be some particular advantage to adding any of these over the others....? don't know
Amino acids in a pure form are actually pretty cheap, so if anyone wants to dose any particular one it would be easy to prep a supplement mix of your choosing....okay....who's first in line?
