Surveying the Genetic and Genomic Diversity of Lentil Nodulating Rhizobia

Lentil (Lens culinaris ssp culinaris) is a pulse legume crop that is an important source of protein for millions of people worldwide. Lentil’s high protein content is a bi-product of its ability to form a symbiotic relationship with several species of nitrogen fixing bacteria from the genus Rhizobium. Rhizobium isolates vary in the efficiency with which they fix nitrogen and consequently bacterial genes and genomes can impact both the vigor and yield potential of the host. The identification of efficient nitrogen fixers that are adapted to different agro-ecological environments may help boost lentil production in a sustainable manner. We are establishing a collection of lentil nodulating bacteria and are implementing WGS to determine the level of genetic and genomic diversity present within our collection. These data will allow us to rationally select diverse strains for greenhouse and field experiments interrogating nitrogen fixation efficiency and strain competitiveness under different field conditions. To date, we have sequenced approximately 150 genomes from strains originating in seven different countries. Our phylogenetic analyses demonstrate significant diversity among the core genomes that appears to be largely a function of the geographic origin of the strains. In contrast, the symbiotic genes are monophyletic relative to other symbiovars, consistent with the horizontal transfer of the symbiosis genes conferring host specificity among different rhizobium species. Our current progress in characterizing the strains and their genomes will be reported.