Bradyrhizobium canariense and Bradyrhizobium japonicum are the two dominant rhizobium species in root nodules of lupin and serradella plants growing in Europe

The genetic diversity of bacterial populations nodulating Lupinus micranthus in five geographical sites from northern Tunisia was examined. Phylogenetic analyses of 50 isolates based on partial sequences of recA and gyrB grouped strains into seven clusters, five of which belong to the genus Bradyrhizobium (28 isolates), one to Phyllobacterium (2 isolates), and one, remarkably, to Microvirga (20 isolates). The largest Bradyrhizobium cluster (17 isolates) grouped with the B. lupini species, and the other five clusters were close to different recently defined Bradyrhizobium species. Isolates close to Microvirga were obtained from nodules of plants from four of the five sites sampled. We carried out an in-depth phylogenetic study with representatives of the seven clusters using sequences from housekeeping genes (rrs, recA, glnII, gyrB, and dnaK) and obtained consistent results. A phylogeny based on the sequence of the symbiotic gene nodC identified four groups, three formed by Bradyrhizobium isolates and one by the Microvirga and Phyllobacterium isolates. Symbiotic behaviors of the representative strains were tested, and some congruence between symbiovars and symbiotic performance was observed. These data indicate a remarkable diversity of L. micranthus root nodule symbionts in northern Tunisia, including strains from the Bradyrhizobiaceae, Methylobacteriaceae, and Phyllobacteriaceae families, in contrast with those of the rhizobial populations nodulating lupines in the Old World, including L. micranthus from other Mediterranean areas, which are nodulated mostly by Bradyrhizobium strains.IMPORTANCE Lupinus micranthus is a legume broadly distributed in the Mediterranean region and plays an important role in soil fertility and vegetation coverage by fixing nitrogen and solubilizing phosphate in semiarid areas. Direct sowing to extend the distribution of this indigenous legume can contribute to the prevention of soil erosion in pre-Saharan lands of Tunisia. However, rhizobial populations associated with L. micranthus are poorly understood. In this context, the diversity of endosymbionts of this legume was investigated. Most Lupinus species are nodulated by Bradyrhizobium strains. This work showed that about half of the isolates from northern Tunisian soils were in fact Bradyrhizobium symbionts, but the other half were found unexpectedly to be bacteria within the genera Microvirga and Phyllobacterium. These unusual endosymbionts may have a great ecological relevance. Inoculation with the appropriate selected symbiotic

Section: Discussionmentioning

confidence: 95%

Diverse Bacteria Affiliated with the Genera Microvirga, Phyllobacterium, and Bradyrhizobium Nodulate Lupinus micranthus Growing in Soils of Northern Tunisia

Msaddak

Durán

Rejili

et al. 2017

“…The presence of two nodA lineages among the isolates nodulating Anthyllis may reflect a different host spectrum or a different symbiotic behavior with Anthyllis or Lotus legumes; these could be two symbiovars within M. metallidurans (the symbiovar loti and another related to Anthyllis). The prevalence of this nodA pattern might be related to the presence of the compatible host plant (A. vulneraria and/or Lotus corniculatus) in their proximate environments, as the legume host can influence the spatial distribution of isolates according to its own geographic distribution (52). Indeed, L. corniculatus was commonly found at the Saint-Bresson (M2 and B2) and M3 sites but not at the M1 mine.…”

Section: Discussionmentioning

confidence: 99%

Ancient Heavy Metal Contamination in Soils as a Driver of Tolerant Anthyllis vulneraria Rhizobial Communities

Mohamad

Maynaud

Quéré

et al. 2017

Anthyllis vulneraria is a legume associated with nitrogen-fixing rhizobia that together offer an adapted biological material for mine-soil phytostabilization by limiting metal pollution. To find rhizobia associated with Anthyllis at a given site, we evaluated the genetic and phenotypic properties of a collection of 137 rhizobia recovered from soils presenting contrasting metal levels. Zn-Pb mine soils largely contained metal-tolerant rhizobia belonging to Mesorhizobium metallidurans or to another sister metal-tolerant species. All of the metal-tolerant isolates harbored the cadA marker gene (encoding a metal-efflux P IB -type ATPase transporter). In contrast, metalsensitive strains were taxonomically distinct from metal-tolerant populations and consisted of new Mesorhizobium genospecies. Based on the symbiotic nodA marker, the populations comprise two symbiovar assemblages (potentially related to Anthyllis or Lotus host preferences) according to soil geographic locations but independently of metal content. Multivariate analysis showed that soil Pb and Cd concentrations differentially impacted the rhizobial communities and that a rhizobial community found in one geographically distant site was highly divergent from the others. In conclusion, heavy metal levels in soils drive the taxonomic composition of Anthyllis-associated rhizobial populations according to their metal-tolerance phenotype but not their symbiotic nodA diversity. In addition to heavy metals, local soil physicochemical and topoclimatic conditions also impact the rhizobial beta diversity. Mesorhizobium communities were locally adapted and site specific, and their use is recommended for the success of phytostabilization strategies based on Mesorhizobium-legume vegetation.IMPORTANCE Phytostabilization of toxic mine spoils limits heavy metal dispersion and environmental pollution by establishing a sustainable plant cover. This ecofriendly method is facilitated by the use of selected and adapted cover crop legumes living in symbiosis with rhizobia that can stimulate plant growth naturally through biological nitrogen fixation. We studied microsymbiont partners of a metaltolerant legume, Anthyllis vulneraria, which is tolerant to very highly metal-polluted soils in mining and nonmining sites. Site-specific rhizobial communities were linked to taxonomic composition and metal tolerance capacity. The rhizobial species Mesorhizobium metallidurans was dominant in all Zn-Pb mines but one. It was not detected in unpolluted sites where other distinct Mesorhizobium species occur. Given the different soil conditions at the respective mining sites, including their heavymetal contamination, revegetation strategies based on rhizobia adapting to local conditions are more likely to succeed over the long term compared to strategies based on introducing less-well-adapted strains.

“…6. Among the 36 strains analyzed, the profiles for strains UPP403, UPP404, UPP407, UPP408, UPP401, UPP409, UPP410, UPP412, UPP413, UPP416, UPP419, UPP422, UPP428, UPP431, and UPP434 (shown in lanes 1,2,5,6,9,12,13,17,18,19,20,22,28,31, and 34, respectively) represented the profile typical for strain USDA 110. The remaining profiles were characteristic of B. japonicum strain USDA 123.…”

Section: Detectionmentioning

confidence: 99%

“…These rhizobia, infecting lupins, are well established in Polish soils. They have colonized the area, presumably migrating together with their hosts from the Mediterranean after the retreat of glaciers during the last 10,000 years (2). These bacteria, however, cannot nodulate soybeans.…”

mentioning

confidence: 99%

Survival and Competitiveness of Bradyrhizobium japonicum Strains 20 Years after Introduction into Field Locations in Poland

Narożna

Pudełko

Króliczak

et al. 2015

Self Cite

bIt was previously demonstrated that there are no indigenous strains of Bradyrhizobium japonicum forming nitrogen-fixing root nodule symbioses with soybean plants in arable field soils in Poland. However, bacteria currently classified within this species are present (together with Bradyrhizobium canariense) as indigenous populations of strains specific for nodulation of legumes in the Genisteae tribe. These rhizobia, infecting legumes such as lupins, are well established in Polish soils. The studies described here were based on soybean nodulation field experiments, established at the Poznań University of Life Sciences Experiment Station in Gorzyń , Poland, and initiated in the spring of 1994. Long-term research was then conducted in order to study the relation between B. japonicum USDA 110 and USDA 123, introduced together into the same location, where no soybean rhizobia were earlier detected, and nodulation and competitive success were followed over time. Here we report the extra-long-term saprophytic survival of B. japonicum strains nodulating soybeans that were introduced as inoculants 20 years earlier and where soybeans were not grown for the next 17 years. The strains remained viable and symbiotically competent, and molecular and immunochemical methods showed that the strains were undistinguishable from the original inoculum strains USDA 110 and USDA 123. We also show that the strains had balanced numbers and their mobility in soil was low. To our knowledge, this is the first report showing the extra-long-term persistence of soybean-nodulating strains introduced into Polish soils and the first analyzing the long-term competitive relations of USDA 110 and USDA 123 after the two strains, neither of which was native, were introduced into the environment almost 2 decades ago.