Host immune suppression as a key adaptation enabling bacterial symbioses

About This Grant

Bacterial symbionts are widespread among animals and plants and often provide beneficial functions that profoundly influence their hosts' biology. Insects, in particular, have repeatedly formed symbioses with microbes for metabolism, nutrition, and protection. Insect immune systems are tasked with the challenge of controlling and regulating beneficial microbes while combating often closely-related pathogenic microbes. A critical unanswered question is whether the insect immune system is a key mediator of both symbionts and pathogens across different host species. This project will combine cutting edge genomics with experimental manipulations that will link immune responses with symbiont associations across diverse host species. Gaining a mechanistic understanding of how immune systems interact with symbionts is not only critical for understanding the evolution of host-associated microbiomes, it also has relevance to the invertebrate pests that vector devastating diseases of crops, livestock, and humans. In addition, there are research opportunities available for undergraduate students to train the next generation of STEM researchers. This project will use aphids as a model system and involves research at the University of Tennessee Knoxville and the Queen Mary University of London. Aphids are uniquely suited for this work because they have strong non-random associations with microbial symbionts: a symbiont species may be common in one aphid species, yet rarely found in a close relative. This suggests a dynamic interplay between host and microbe that can drive symbiont spread or loss over relatively short evolutionary timescales. Preliminary data has shown that hosting certain symbionts leads to a sharp decrease in the expression of key immune genes in aphids. This suggests host immunity is of central importance to the evolution of symbiotic relationships. The primary objective of this project is to use transcriptome sequencing and immune assays to test the hypothesis that host immune suppression is a key mechanism explaining the distribution of symbiotic microbes across aphid species. A secondary objective is to determine whether there is a trade-off in the ability to harbor symbionts and resist pathogens across species. Genomes of virulent and non-virulent symbiont strains will also be compared using a novel symbiont culturing technology to identify genetic features that underlie pathogenicity in symbiotic microbes. Together, this cross-species approach will transform our understanding of how host immunity moderates relationships with symbiotic microbes. This project will thus provide key insight into how invertebrates form and maintain relationships with microbes that can drive rapid adaptive evolution in species of central importance to food security and health. This collaborative US/UK project is supported by the US National Science Foundation and the UK Biotechnology and Biological Sciences Research Council. 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.