Beneficial bacteria that live inside insect cells are widespread in nature and have persisted in partnerships with their hosts for tens to hundreds of millions of years. Despite their importance – many insects cannot survive or reproduce without them – scientists know surprisingly little about how host cells maintain normal function while housing a resident bacterium, or how bacteria are reliably passed from mother to offspring generation after generation. This project investigates these questions using the pea aphid and its bacterial partner Buchnera aphidicola, one of the best-studied examples of this type of ancient partnership. Understanding how host cells regulate their bacterial residents has broad relevance across biology, from explaining how animals coexist with beneficial microbes to inspiring future biotechnologies that harness microbes to improve agricultural productivity, advance the national health and increase food security. The project will train graduate and undergraduate students in genomics, advanced microscopy, and evolutionary biology, and will support development of freely available classroom materials on symbiosis and cell biology for middle school students in Florida, aligned to state science standards.
This project tests the hypothesis that the mechanistic target of rapamycin Complex 1 (mTORC1) – a conserved signaling pathway that integrates nutrient availability with cell growth and autophagy – functions as a master regulator of the pea aphid’s partnership with Buchnera. Prior work demonstrated that mTORC1 genes are upregulated in the specialized cells that house Buchnera, and that chemical inhibition of mTORC1 reduces aphid reproduction and disrupts symbiont population size and host cell morphology. Two objectives are proposed: (1) determining how mTORC1 regulates Buchnera population size in post-embryonic aphids, and (2) determining whether mTORC1 governs Buchnera transmission and integration during embryonic development. Both objectives combine chemical inhibition and activation of mTORC1 with confocal microscopy, droplet digital PCR for ploidy-independent quantification of symbiont genome copy number, and transcriptomics of both host and symbiont. A central methodological contribution is the extension of SymbiQuant – a deep neural network tool developed by the research team that automates detection and quantification of individual bacterial cells within host tissue – to embryonic tissues, producing an updated pipeline capable of characterizing symbiont transmission across developmental stages. This advance in AI-assisted biological image analysis will be made openly available to the broader community studying intracellular symbioses.
This award reflects NSF’s statutory mission and has been deemed worthy of support through evaluation using the Foundation’s intellectual merit and broader impacts review criteria.