Aphids are pests that threaten food security, causing millions of pounds of damage to crops in the UK alone. Because they live exclusively on the sugary sap of plants, their diets only contain limited amounts of nitrogenous essential amino acids. To solve this problem, the aphid has a symbiotic bacterium, called Buchnera, living inside some of its cells that supplements the animal's diet with the required nutrients.

Today, the researchers from the Department of Biology at the University of York, and their partners from Cornell University in the USA publish a significant advance in our understanding of how this symbiosis works by studying the specific adaptations in the specialised bacteriocyte cells that have evolved to house the bacteria.

The UK researchers were funded by the Biotechnology and Biological Sciences Research Council (BBSRC).

By using computational modelling of the metabolism of the symbiotic bacteria, combined with experimental data, the scientists have revealed an unexpected twist in the metabolic basis of the symbiosis, namely that it is the insect cells that recycle nitrogen to build essential amino acids, rather than the bacterial cells themselves as previously thought. The work also demonstrates that the overall metabolism of the bacteriocyte has evolved to provide for the metabolic demands of its partner and also to recycle waste products produced by Buchnera metabolism.

Project lead at the University of York, Gavin Thomas, Ph.D., said, "The research reveals enzymes that are needed by the aphid to manage its bacterial smbionts, thus also providing potential targets for aphid-specific insecticides.

On the approach that was used, he added, "The project is a great example of the possibilities of systems biology, integrating transcriptomics, proteomics, metabolic models and flux balance analysis to propose and test novel hypotheses about the way these two organisms interact."

The work is published in the current issue of the Proceedings of the Royal Society B: Biological Science and was led by Sandy Macdonald, Ph.D., a postdoctoral researcher in Thomas's laboratory at York working with collaborators led by Professor Angela Douglas at Cornell University.

The paper 'The central role of the host cell in symbiotic nitrogen metabolism' is published at rspb.royalsocietypublishing.org/content/early/2012/04/17/rspb.2012.0414.abstract.