Do gut immune responses drive evolution of the gut microbiome?
Lead Research Organisation:
University of Liverpool
Department Name: Evolution, Ecology and Behaviour
Abstract
Our idea is that gut antibody responses that target a sub-set of bacterial cells in the gut microbiome drive the evolution of those bacteria so that they evolve faster than bacteria not targeted by the gut antibody response. We now propose to test this idea.
Background and rationale. The gut microbiome - the assemblage of bacteria in the gut - has profound effects on the lives of people and animals, and so it matters what bacterial taxa and strains comprise the microbiome.
Hitherto, the focus of studying the composition of the microbiome has been on where bacteria are acquired from, and on the effect of the diet and gut physiology of the host. Our novel idea is that host immune responses drive the evolution of bacteria in the microbiome, changing the microbiome's composition, and so affecting animal and human health.
The mammalian gut has a fully functioning immune response, and mounts an immunoglobulin A (IgA) antibody response in the gut lumen. Approximately 20% of bacterial cells in the gut are bound by IgA - henceforth "IgA+ bacteria". The vast majority of these IgA+ bacteria are commensal bacteria, not pathogens. We propose that IgA acts as a selective force driving the evolution of IgA+ bacteria so that they have a different mode and tempo of evolution compared with IgA- bacteria. Because bacteria have a very short generation time compared with their hosts, this IgA-driven evolution occurs during the host's life.
We propose this immune-driven evolution because there are many well-known examples of microbial pathogens where immune responses select against certain antigenic types, so that new antigenic types evolve to escape the immune responses; examples are Streptococcus pneumoniae, Neisseria meningitidis, Staphylococcus aureus, and Plasmodium falciparum - the malaria parasite. Our hypothesis is that analogous processes occur for IgA+ bacteria in the gut microbiome, changing its composition.
Background and rationale. The gut microbiome - the assemblage of bacteria in the gut - has profound effects on the lives of people and animals, and so it matters what bacterial taxa and strains comprise the microbiome.
Hitherto, the focus of studying the composition of the microbiome has been on where bacteria are acquired from, and on the effect of the diet and gut physiology of the host. Our novel idea is that host immune responses drive the evolution of bacteria in the microbiome, changing the microbiome's composition, and so affecting animal and human health.
The mammalian gut has a fully functioning immune response, and mounts an immunoglobulin A (IgA) antibody response in the gut lumen. Approximately 20% of bacterial cells in the gut are bound by IgA - henceforth "IgA+ bacteria". The vast majority of these IgA+ bacteria are commensal bacteria, not pathogens. We propose that IgA acts as a selective force driving the evolution of IgA+ bacteria so that they have a different mode and tempo of evolution compared with IgA- bacteria. Because bacteria have a very short generation time compared with their hosts, this IgA-driven evolution occurs during the host's life.
We propose this immune-driven evolution because there are many well-known examples of microbial pathogens where immune responses select against certain antigenic types, so that new antigenic types evolve to escape the immune responses; examples are Streptococcus pneumoniae, Neisseria meningitidis, Staphylococcus aureus, and Plasmodium falciparum - the malaria parasite. Our hypothesis is that analogous processes occur for IgA+ bacteria in the gut microbiome, changing its composition.
