Community structure of known and previously unknown endobacteria associated with spores of arbuscular mycorrhizal fungi

Abstract

AbstractArbuscular mycorrhizal fungi (AMF) are ubiquitous plant root symbionts which can house two endobacteria:Ca.Moeniiplasma glomeromycotorum (CaMg) andCa. Glomeribacter gigasporarum (CaGg). However, little is known about their distribution and population structure in natural AMF populations and whether AMF can harbour other endobacteria. We isolated AMF from two environments and surveyed the surface-sterilized spores for endobacteria. We found thatCaMg andCaGg differed significantly in distribution wherebyCaMg were extremely abundant (80%) andCaGg were extremely rare (2%) in both environments. Unexpectedly, we discovered an additional and previously unknown level of bacterial diversity within AMF spores which extended beyond the known endosymbionts, with as many as 277 other bacterial taxa detected in individual spores. Detailed analysis of endobacterial communities inside AMF spores revealed that: (i)CaGg were not limited in distribution to theGigasporaceafamily of AMF, as previously thought, (ii)CaMg community structure was driven by AMF host genotype, (iii) a significant inverse correlation existed between the diversity ofCaMg and diversity of all other endobacteria. The latter suggests the existence of competition dynamics between different bacterial populations inside AMF spores and provides a basis for generation of testable hypotheses regarding the function ofCaMg in AMF biology.