CAREER: Mechanisms and evolution of defensive microbial symbiosis in insects

This award is funded in whole or in part under the American Rescue Plan Act of 2021 (Public Law 117-2).

All organisms face threats from parasites and pathogens and have evolved specialized immune responses for protection. Parasites respond in turn with modifications to their own genetic weaponry to more effectively avoid or disable host defenses. Recent research has emphasized the importance of a third player in infections, the host’s microbial allies, which can provide strong protection against invaders.

However, central question about the activities and effects of symbionts on hosts and parasites remain to be answered. For instance, how do symbionts target and disable many different types of parasites without harming the host? How do defensive genes influence the back-and-forth “arms race” between host defenses and parasite resistance?

A goal of this research is to answer these open questions through molecular and genetic investigations of an exemplar symbiosis between the fruit fly, Drosophila, and Spiroplasma, a bacterial partner that defends it against internal parasites. The project will also collaborate with Mississippi State University students and school teachers, providing training in bacterial evolution and cutting-edge genome sequencing technology while investigating symbiont-parasite interactions in natural insect populations.

As research organisms, insects offer ideal systems to experimentally investigate fundamental questions about these partnerships and the genes that support them, and as pollinators, consumers, pests, and disease vectors, insects are deeply connected to their natural ecosystems, and to human health and food security. Therefore, this research will contribute to advancing knowledge in the areas of parasite-host interactions, bacterial evolution, and insect ecology.

Conflict between parasite and host is a key driver of natural selection, reshaping life history strategies, immune systems, and virulence factors across all biological organisms. While defensive microbial symbionts are increasingly recognized as fundamental contributors to host ecology, the molecular evolutionary context underlying their place in the parasite-host arms race is not well understood.

This project aims to address this gap through functional genetic studies of a model insect defensive symbiosis. Bacterial toxins encoded by Spiroplasma help defend Drosophila hosts against parasitic wasps and nematodes, and exhibit rapid molecular evolution, frequent recombination, and conjugative mobilization across the symbiont genus. Multiple origins of resistance within wasps complements these dynamic patterns of toxin evolution, suggesting arms race-like coevolutionary processes may underlie symbiont-parasite interactions.

This project’s research goals are to 1) determine the molecular basis of parasite-specific defenses by Spiroplasma, 2) characterize novel genotype and phenotype diversity of defensive strains, and 3) identify mechanisms of resistance to Spiroplasma-mediated defense. These research goals will be extended through an educational partnership with students at Mississippi State University to investigate symbiont toxin evolution and parasite resistance dynamics in local field populations.

Finally, this award will support development of a bacterial genomics laboratory module for biology teachers in Mississippi and neighboring states as part of their graduate degree training. These activities will enable and promote a deeper understanding of molecular evolutionary mechanisms, biotechnology, and bioinformatics in classrooms throughout the state and region.

This project is jointly funded by the Symbiosis, Infection and Immunity Program in the Division of Integrative Organismal Systems in the Directorate of Biological Sciences and by the Established Program to Stimulate Competitive Research (EPSCoR).

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.