A metabolic study of Buchnera, the intracellular bacterial symbionts of the pea aphid Acyrthosiphon pisum

Abstract

Cells of the bacterium Buchnera were isolated from embryos of the pea aphid Acyrthosiphon pisum, with an intact perisymbiont membrane (the insect membrane which surrounds each bacterial cell inside the aphid). The bacterial preparations respired aerobically, consuming oxygen at an average rate of 24 nmol (mg protein)−1 min−1. The bacteria took up a range of carboxylic acids and the amino acids glutamate and aspartate from an external concentration of 0·5 mm at rates of 1–10 nmol (mg protein)−1 h−1; glucose was taken up at 0·17 nmol (mg protein)−1 h−1. Glutamate uptake was proportional to its external concentration, at all concentrations tested between 15 μm and 10 mm. Saturable systems for the uptake of succinate and aspartate were identified. The kinetic constants were: K m 0·79 mm, V max 12·6 nmol (mg protein)−1 min−1 for succinate; and K m 0·22 mm, V max 3·3 nmol (mg protein)−1 min−1 for aspartate. Succinate uptake was not inhibited by the uncoupler CCCP and was markedly stimulated by ATP, suggesting that its transport is not linked to a proton-motive force but is dependent on an energized membrane and possibly mediated by a co-transport system involving another ion.