Quantifying nutrient production by the microbial symbionts in an aphid

Area of Science:

• Microbiology
• Insect Physiology
• Symbiotic Relationships

Background:

• Aphids rely on symbiotic bacteria, Buchnera sp., for essential amino acids absent in their phloem sap diet.
• Understanding the contribution of these bacterial symbionts to aphid nutrition is crucial for insect physiology research.

Purpose of the Study:

• To quantify the contribution of Buchnera-derived amino acids to the net protein growth of the aphid Aphis fabae.
• To investigate the metabolic relationship between aphids and Buchnera sp., particularly regarding amino acid synthesis and assimilation.

Main Methods:

• Quantified aphid protein growth on chemically defined diets lacking individual essential amino acids.
• Utilized metabolic analysis with dietary [(14)C]glutamic acid to trace amino acid incorporation in aphids.
• Experimentally deprived aphids of Buchnera sp. (aposymbionts) to assess their independent amino acid synthesis capabilities.

Main Results:

• Buchnera sp. produced essential amino acids at rates varying from 8-156 pmol µg(-1)protein day(-1).
• Aphids incorporated dietary [(14)C]glutamic acid into essential amino acids, with incorporation into isoleucine increasing when dietary isoleucine was omitted.
• Aposymbiotic aphids showed high mortality on phenylalanine-free diets and reduced leucine assimilation, indicating dependence on Buchnera for essential amino acids.

Conclusions:

• Buchnera sp. significantly contributes to aphid protein growth by supplying essential amino acids.
• Dietary amino acid availability can influence Buchnera's biosynthetic rates, suggesting a dynamic symbiotic interaction.
• The absence of Buchnera-derived amino acids and inefficient assimilation of certain dietary amino acids severely impair aphid growth and survival.