Abstract
Lupinus is known to form endophytic associations with both nodulating and non-nodulating bacteria. In this study, multilocus sequence analysis (MLSA) was used to analyze phylogenetic relationships among root nodule bacteria associated with Lupinus and soybean. Out of 17 bacterial strains analyzed, 13 strains isolated from root nodules of Lupinus spp. were obtained from the National Rhizobium Germplasm Resource Collection, USDA. Additionally, two strains of root-nodule bacteria isolated each from native lupinus and domestic soybean were examined. Sequences of the 16S rRNA gene and three house-keeping genes (atpD, dnaK and glnII) were used. All the reference genes were retrieved from the existing complete genome sequences only. The clustering of 12 of the strains was consistent among single and concatenated gene trees, but not USDA strains 3044, 3048, 3504, 3715, and 3060. According to the concatenated phylogeny, we suggest that USDA 3040, 3042, 3044, 3048, 3051, 3060, 3504, 3709 and 3715 are Bradyrhizobium, USDA 3063 and 3717 are Mesorhizobium, USDA 3043 is Burkholderia and USDA 3057a is Microvirga. The two strains isolated from native lupines in this study are Burkholderia and Rhizobium, whereas the two from domestic soybean are Bradyrhizobium. This study emphasizes the robustness of MLSA, the diversity of bacterial species that are capable of nodulating lupine and the substantial capability of Burkholderia spp. to colonize lupine root nodules.
Highlights
According to the concatenated phylogeny, we suggest that USDA 3040, 3042, 3044, 3048, 3051, 3060, 3504, 3709 and 3715 are Bradyrhizobium, USDA 3063 and 3717 are Mesorhizobium, USDA 3043 is Burkholderia and USDA 3057a is Microvirga
This study emphasizes the robustness of multilocus sequence analysis (MLSA), the diversity of bacterial species that are capable of nodulating lupine and the substantial capability of Burkholderia spp. to colonize lupine root nodules
The rhizobial requirement of Lupinus has been thought to be somewhat specific, with literature indicating that lupines are mainly nodulated by soil bacteria classified in the genus Bradyrhizobium, some other rhizobial and endophytic genera nodulating lupines have been identified as Mesorhizobium, Rhizobium, Microvirga, Paenibacillus, Micromonospora, Bosea, Ochrobactrum and Cohnella [2]-[14]
Summary
Within the Genisteae tribe of the legume subfamily Faboideae, the genus Lupinus or lupine encompasses more than 280 species of annual herbs and perennial herbaceous and woody shrubs distributed mainly in South and Western North America, the Andes, the Mediterranean regions and Africa [1]. Because of this ability to establish symbiotic associations with bacteria that can fix atmospheric nitrogen in root nodules, members of the genus Lupinus thrive in nutrient poor soils. Members of the genus Burkholderia (in class Betaproteobacteria) are known as endophytic bacteria in lupine [15] and considered the major inhabitants of white lupine cluster roots [16]
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