The Metabolome of Associations between Xylem-Feeding Insects and their Bacterial Symbionts

Metabolomics has increasingly led to important insights in chemical ecology by identifying environmentally relevant small molecules that mediate inter-organismal interactions. Nevertheless, the application of metabolomics to investigate interactions between phytophagous insects and their microbial symbionts remains underutilized. Here, we investigated the metabolomes of the bacteriomes (organs bearing symbiotic bacteria) isolated from natural populations of five species of xylem-feeding insects. We identified three patterns. First, the metabolomes varied among the five species, likely influenced by insect phylogeny, food plant and taxonomic identity of the symbionts. Second, the ratio of glutamine: glutamate in the bacteriomes was 0.7–3.6 to 1, indicative of nitrogen-sufficient metabolism and raising the possibility that the insect sustains nitrogen-enriched status of the bacteriomes despite the nitrogen scarcity of the xylem diet. Finally, bacteriomes from insect species bearing genetically-similar symbionts displayed limited variation in their metabolomes, suggesting that the metabolic pattern of the bacteriome metabolic pools is correlated with the genetic repertoire of the symbionts. Altogether, these metabolomic patterns yield specific hypotheses of underlying processes that are testable by wider sampling of natural populations and experimental study.