Lipid metabolism in the aphid-Buchnera symbiosis: an underexplored dimension of insect physiology.
Source: PubMed, NCBI / U.S. National Library of Medicine
Lipids are essential biomolecules that function as energy reserves, signaling mediators, and structural components of cellular membranes, yet their roles in insect-microbe symbiosis remain poorly understood. In contrast to the well-established contributions of microbial symbionts to amino acid and vitamin metabolism, symbiotic lipid metabolism has received comparatively little attention. Here, we review current knowledge of lipid metabolism in insect symbiosis, focusing on the aphid-Buchnera association as a model of obligate mutualism. Physiological evidence indicates that aphids rely primarily on dietary sterols and endogenous fatty acid synthesis rather than on lipid provisioning by Buchnera. Genomic analyses reveal that Buchnera has lost most canonical genes required for de novo fatty acid synthesis, unsaturated fatty acid production, phospholipid biosynthesis, and fatty acid degradation, while retaining a minimal set of lipid-related functions, most notably cls, encoding a cardiolipin synthase homolog. A functional study further demonstrates that cls is essential for symbiont integrity and host fitness. The aphid host retains a complete lipid biosynthetic capacity and exhibits expansion of key gene families, suggesting a host-dominated metabolic organization. This asymmetric gene repertoire prompts a membrane paradox: Buchnera retains cellular membranes despite near-complete phospholipid auxotrophy. We also discuss how intracellular pathogenic bacteria provide conceptual
Abstract
Lipids are essential biomolecules that function as energy reserves, signaling mediators, and structural components of cellular membranes, yet their roles in insect-microbe symbiosis remain poorly understood. In contrast to the well-established contributions of microbial symbionts to amino acid and vitamin metabolism, symbiotic lipid metabolism has received comparatively little attention. Here, we review current knowledge of lipid metabolism in insect symbiosis, focusing on the aphid-Buchnera association as a model of obligate mutualism. Physiological evidence indicates that aphids rely primarily on dietary sterols and endogenous fatty acid synthesis rather than on lipid provisioning by Buchnera. Genomic analyses reveal that Buchnera has lost most canonical genes required for de novo fatty acid synthesis, unsaturated fatty acid production, phospholipid biosynthesis, and fatty acid degradation, while retaining a minimal set of lipid-related functions, most notably cls, encoding a cardiolipin synthase homolog. A functional study further demonstrates that cls is essential for symbiont integrity and host fitness. The aphid host retains a complete lipid biosynthetic capacity and exhibits expansion of key gene families, suggesting a host-dominated metabolic organization. This asymmetric gene repertoire prompts a membrane paradox: Buchnera retains cellular membranes despite near-complete phospholipid auxotrophy. We also discuss how intracellular pathogenic bacteria provide conceptual frameworks for host-supported lipid acquisition and membrane maintenance. Finally, we highlight emerging opportunities offered by host-symbiont lipidomics for dissecting lipid interactions and membrane-centered metabolic integration in intracellular life.