Endosymbiotic bacteria in mycorrhizal fungi: from their morphology to genomic sequences

Arbuscular mycorrhizal (AM) fungi have been successful in time and space thanks to a long co-evolution with their host plants. In addition to this well known interaction, they also associate with bacteria that reside in the fungal cytoplasm. The chapter mostly focusses on endosymbionts belonging to the genus Burkholderia and found in many species of Gigasporaceae. We have used morphological and genetic approaches to investigate these intracellular microrganisms. Some genes related to metabolism, cell colonization events and nitrogen fixation have been characterized and suggest a potential role in the nutritional exchanges between endobacteria, fungi and plants.