Uric acid deposits in symbiotic marine algae.

The symbiosis between cnidarians and dinoflagellate algae is not understood at the cell or molecular level, yet this relationship is responsible for the formation of thousands of square kilometres of coral reefs. We have investigated the nature of crystalline material prominent within marine algal symbionts of Aiptasia sp. anemones. This material, which has historically been considered to be calcium oxalate, is shown to be uric acid. We demonstrate that these abundant uric acid stores can be mobilized rapidly, thereby allowing the algal symbionts to flourish in an otherwise N-poor environment. This is the first report of uric acid accumulation by symbiotic marine algae. These data provide new insight and considerations for understanding the physiological basis of algal symbioses, and represent a new and previously unconsidered aspect of N metabolism in cnidarian, and a variety of other, marine symbioses.