Buchnera

Buchnera is a genus of Gram-negative, obligate intracellular bacteria that live in specialized aphid cells called bacteriocytes, clustered within the aphid’s bacteriome. The best-known member, Buchnera aphidicola, is the primary endosymbiont of most aphids and forms a long-standing mutualistic association with its host. The bacteria provide essential amino acids that are scarce in the aphid’s diet of phloem sap, while the aphid supplies a protected intracellular niche and resources needed for bacterial replication.

Genomic features reflect its long-term intracellular lifestyle. Buchnera has undergone extensive genome reduction, retaining a compact set of genes centered on amino acid biosynthesis and other functions critical for the symbiosis. The genome is small (on the order of 0.6 megabases) and highly streamlined, with many genes lost or inactivated as pseudogenes. Despite the reduction, Buchnera continues to synthesize several essential amino acids for the aphid, and the metabolic complementarity with the host depends on transport of amino acids and metabolites between the two partners.

Ecology and transmission: Buchnera resides in specialized host cells called bacteriocytes and is vertically transmitted from mother to offspring through the eggs. The aphid–Buchnera association shows a high degree of co-evolution, with aphid lineages often carrying lineage-specific Buchnera strains. In most aphids, Buchnera is not cultivable outside the host under standard laboratory conditions.

Significance: Buchnera is a classic model for studying obligate insect endosymbiosis, genome reduction, and the evolution of mutualism. It has informed understanding of how symbiotic relationships enable herbivorous insects to exploit nutrient-poor diets.