Essential amino acid synthesis and nitrogen recycling in an alga-invertebrate symbiosis

When aseptically-cultured sea anemones, Aiptasia pulchella, were incubated with C-14-labelled glucose, aspartate and glutamate, radioactivity was inco rporated into animal protein. Radioactivity was recovered from all amino ac ids in the protein hydrolysates of A. pulchella bearing the symbiotic alga Symbiodinium sp., and from all but seven of the amino acids in A. pulchella experimentally deprived of their algae. These data suggest that these seve n amino acids (histidine, isoleucine, leucine, lysine, phenylalanine, tyros ine and valine) may be synthesized by the symbiotic algae and translocated to the sea anemone's tissues; and that methionine and threonine, two amino acids traditionally considered as dietary essentials for animals, are synth esized by A. pulchella. Essential amino acid translocation from the symbiot ic algae to the animal host is a core element in symbiotic nitrogen-recycli ng. Its nutritional value to the animal host is considered in the context o f the amino acid biosynthetic capacity of the host.