New chromosomal lineages within Microvirga and Bradyrhizobium genera nodulate Lupinus angustifolius growing on different Tunisian soils

Abstract

Thirty-one rhizobial isolates nodulating native Lupinus angustifolius (blue lupine) plants growing in Northern Tunisian soils were isolated and analysed using different chromosomal and symbiotic gene markers. Phylogenetic analyses based on recA partial sequences grouped them into at least five groups: four of them within the genus Bradyrhizobium (26 isolates) and one into the genus Microvirga (5 isolates). Representative strains were analysed by multilocus sequence analysis of three housekeeping genes rrs-recA-glnII and rrs-gyrB-dnaK for Bradyrhizobium and Microvirga isolates, respectively. Based on this analysis, eight isolates clustered with the previously described strains Bradyrhizobium lupini USDA3051 and Bradyrhizobium canariense BTA-1. However, five of the isolates clustered separately and may constitute a new species within the Bradyrhizobium genus. The remaining five isolates were closely related to the strain Microvirga sp. LmiM8 and may constitute a new Microvirga species. The analysis of the nodC gene showed that all Bradyrhizobium strains nodulating blue lupine belong to the symbiovar genistearum, whereas the Microvirga isolates are associated with the symbiovar mediterranense. The results of this study support that the L. angustifolius root nodule symbionts isolated in Northern Tunisia belong mostly to the B. canariense/B. lupini lineages. However, new clades of Bradyrhizobium and Microvirga have been identified as L. angustifolius endosymbionts.

Microvirgasp. symbiovar mediterranense nodulatesLupinus cosentiniigrown wild in Morocco

“…, ; Rejili et al . ). The results showed that the isolates from L. cosentinii belong to genus Microvirga and that LmiE10 and LmiM8 isolated from L. micranthus are the closest relative strains based on phylogenies of housekeeping genes.…”

“…) and L. angustifolius (Rejili et al . ) emphasize the capability of Microvirga to colonize lupine root nodules. Indeed, Bradyrhizobium has been isolated from root nodules of L. cosentinii in Morocco (Thami Alami et al .…”

“…, ; Rejili et al . ) and suggests that the soil pH is a key factor for determination of the biogeography of the Microvirga species. In contrast to Microvirga , Bradyrhizobium appears to be dominant in acidic to neutral soils (Stepkowski et al .…”

“…To confirm the taxonomic status of the L. cosentinii-isolated strains, phylogenetic trees based on the housekeeping concatenated 16S rRNA, dnaK, gyrB and recA sequences were built. The sequences of those genes have been used previously for identification of Microvirga (Ardley et al 2012;Radl et al 2014;Veyisoglu et al 2016;Msaddak et al 2017aMsaddak et al , 2017bRejili et al 2019). The results showed that the isolates from L. cosentinii belong to genus Microvirga and that LmiE10 and LmiM8 isolated from L. micranthus are the closest relative strains based on phylogenies of housekeeping genes.…”

“…3) grouped the four LUP strains with Microvirga sp. strains LmiE10, LmiM8, and aBH2, members of the symbiovar mediterranense recently described by Msaddak et al (2018) and Rejili et al (2019).…”