Competition Experiments for Legume Infection Identify as a Highly Competitive β-Rhizobium.

Members of the genus (β-proteobacteria) have only recently been shown to be able to establish a nitrogen-fixing symbiosis with several legumes, which is why they are also referred to as β-rhizobia. Therefore, very little is known about the competitiveness of these species to nodulate different legume host plants. In this study, we tested the competitiveness of several type strains (, , , , and ) to nodulate four legumes (, , and ) under our closely defined growth conditions. The assessment of nodule occupancy of these species on different legume host plants revealed that was the most competitive strain in the three papilionoid legumes (bean, cowpea and siratro), while outcompeted the other strains in mimosa. The analysis of phenotypes known to play a role in nodulation competitiveness (motility, exopolysaccharide production) and additional competition assays among β-rhizobial strains suggested that has the potential to be a very competitive legume symbiont.