Metabolic fate of energetic amino acids in the aposymbiotic pea aphid Acyrthosiphon pisum (Harris) (Homoptera: Aphididae)

Amino acid metabolism of aposymbiotic pea aphids obtained by an antibiotic treatment was analysed by the use of C-14-radiolabeled tracers in isotopic equilibrium, and compared with data obtained previously in symbiotic conditions. The interconversions between energetic amino acids were little affected, but the synthesis of three essential amino acids (threonine, isoleucine and lysine) from carbons of common amino acids was interrupted after antibiotic treatment. An accumulation of glutamate from precursors normally converted to these essential amino acids and an increase of glutamate or glutamine in the honeydew plus exuviae of aposymbiotic aphids were likewise observed. These results validate the role of the symbiotic bacteria in the synthesis of essential amino acids.