Inter- and intraspecific variation within the morphologically similar arbuscular mycorrhizal fungi Glomus mosseae and Glomus coronatum

This collaborative investigation was aimed at using morphological and molecular characters to study inter- and intraspecific variation within isolates of Glomus mosseae and Glomus coronatum from different parts of the world. A secondary aim was to assess whether any divergence found was genetically based and/or correlated with the biogeographic origin of isolates. Morphological evaluations of various possible taxonomic characters including spore colour, size, sporocarp architecture and hyphal attachment morphology, showed that only spore colour could discriminate the two groups. Isozyme analysis of malate dehydrogenase and esterase loci clearly confirmed this grouping of the two species complexes. SDS profiles and cluster analysis showed the same separation on a selection of isolates from the two groups. A comparison of a representative isolate from the G. coronatum group (BEG 49) with other arbuscular mycorrhizal fungi using G. mosseae-specific primers also provided evidence for separation of the two species complexes. The data and methodology employed provide a blueprint for future multimodal and multidisciplinary approaches to the unravelling of taxonomic problems within this ancient group of symbiotic fungi

Detection of a novel intracellular microbiome hosted in arbuscular mycorrhizal fungi

Arbuscular mycorrhizal fungi (AMF) are important members of the plant microbiome. They are obligate biotrophs that colonize the roots of most land plants and enhance host nutrient acquisition. Many AMF themselves harbor endobacteria in their hyphae and spores. Two types of endobacteria are known in Glomeromycota: rod-shaped Gram-negative Candidatus Glomeribacter gigasporarum, CaGg, limited in distribution to members of the Gigasporaceae family, and coccoid Mollicutes-related endobacteria, Mre, widely distributed across different lineages of AMF. The goal of the present study is to investigate the patterns of distribution and coexistence of the two endosymbionts, CaGg and Mre, in spore samples of several strains of Gigaspora margarita. Based on previous observations, we hypothesized that some AMF could host populations of both endobacteria. To test this hypothesis, we performed an extensive investigation of both endosymbionts in G. margarita spores sampled from Cameroonian soils as well as in the Japanese G. margarita MAFF520054 isolate using different approaches (molecular phylotyping, electron microscopy, fluorescence in situ hybridization and quantitative real-time PCR). We found that a single AMF host can harbour both types of endobacteria, with Mre population being more abundant, variable and prone to recombination than the CaGg one. Both endosymbionts seem to retain their genetic and lifestyle peculiarities regardless of whether they colonize the host alone or together. These findings show for the first time that fungi support an intracellular bacterial microbiome, in which distinct types of endobacteria coexist in a single cell