Comparative genomics of photosynthetic bradyrhizobia

Tropical aquatic species of the legume genus Aeschynomene are stem and root-nodulated by bradyrhizobia exhibiting atypical features (bacterial photosynthesis, use of a nod-dependent (ND) or a nod-independent (NI) pathway to enter into symbiosis). In this study we used a comparative genomics approach on 9 Aeschynomene symbionts representative of the phylogenetic diversity of Aeschynomene symbionts published in Miché et al (2010). We produced draft genomes of a set of strains representing different phenotypes: 5 NI photosynthetic strains (STM3809, ORS375, STM3847, STM4509, STM4523) in addition to the previously sequenced ORS278 and BTAi1 genomes (Giraud et al., 2007), 1 photosynthetic strain ORS285 hosting both ND and NI symbiotic systems, and 1 NI non-photosynthetic strain (STM3843). Comparative genomics allowed to infer the core, pan and dispensable genomes of Aeschynomene bradyrhizobia, and to detect specific genes and their location into Genomic islands (GI). Comparative gene sets depending on the photosynthetic and NI/ND abilities allowed to list putative genes involved in these phenotypes, that were linked to functional analyses currently under way.