An interaction between host and microbe genotypes determines colonization success of a key bumble bee gut microbiota member

There has been a proliferation of studies demonstrating an organism’s
health is influenced by its microbiota. However, factors influencing
beneficial microbe colonization and the evolution of these relationships
remain understudied relative to host-pathogen interactions. Vertically
transmitted beneficial microbes are predicted to show high levels of
specificity in colonization, including genotype matching, which may
transpire through coevolution. We investigate how host and bacterial
genotypes influence colonization of a core coevolved microbiota member in
bumble bees. The hindgut colonizing Snodgrassella alvi confers direct
benefits, but, as an early colonizer, also facilitates the further
development of a healthy microbiota. Due to predominantly vertical
transmission promoting tight evolution between colonization factors of
bacteria and host lineages, we predict that genotype-by-genotype
interactions will determine successful colonization. Germ-free adult bees
from seven bumble bee colonies (host genotypic units) were inoculated with
one of six genetically distinct strains of S. alvi. Subsequent
colonization within host-genotype and microbe-genotype combinations ranged
from zero to one hundred percent, and an interaction between host and
microbe genotypes determined colonization success. This novel finding of a
genotype-by-genotype interaction determining colonization in an animal
host-beneficial microbe system has implications for the ecological and
evolutionary dynamics of host and microbe, including associated
host-fitness benefits.