Identification of signature motifs for monitoring Candidatus Glomeribacter gigasporarum and its mycorrhizal fungal host

The Fungal Kingdom offers a limited number of examples of endobacteria living in fungal cytoplasm. Arbuscular mycorrhizal (AM) fungi, are themselves obligate plant symbionts but provide one of the best known study-cases, being specialised niches for rod-shaped bacteria that are vertically transmitted through the vegetative generations (Bianciotto et al. 2004 AEM). On the basis of their ribosomal sequences, the endobacteria have been identified as a new bacterial taxon, Candidatus Glomeribacter gigasporarum (Bianciotto et al . 2003 IJESM). Their morphological features confirm them as Gram-microbes with a highly reduced genome evaluated as 1.4 Mbs and consisting of a chromosome and a plasmid (Jargeat et al. 2004 J. Bacteriol.). The status of uncultivable microbe and the reduced genome size strongly suggest that Ca. Glomeribacter gigasporarum is an obligate endosymbiont (Lumini et al. 2007 Cell. Microbiol.).