Diversity and Efficiency of Rhizobia Communities from Iron Mining Areas Using Cowpea as a Trap Plant

<div><p>ABSTRACT Mining is an important economic activity. However, its impact on environment must be accessed, mainly on relevant processes for their sustainability. The objective of this study was to evaluate the diversity and efficiency of symbiotic nitrogen fixing bacterial communities in soils under different types of vegetation in the Quadrilátero Ferrífero: ironstone outcrops, Atlantic Forest, neotropical savanna, and a rehabilitated area revegetated with grass. Suspensions of soil samples collected under each type of vegetation were made in a saline solution to capture rhizobia communities that were then inoculated on cowpea [Vigna unguiculata (L.) Walp.], which was used as a trap plant. The symbiotic efficiency of the communities was evaluated in a greenhouse experiment and the data obtained were correlated to the chemical and physical properties of the soils under each type of vegetation. At the end of the experiment, the bacteria present in the nodules were isolated to evaluate their diversity. The highest numbers of nodules occurred in the treatment inoculated with soil samples from rehabilitated area revegetated with grass and neotropical savanna vegetation, and the lowest numbers were observed in the treatment inoculated with soil samples from ironstone outcrops and Atlantic Forest. In relation to root dry matter, the treatment inoculated with soil samples from Neotropical savanah was superior to those inoculated with soil samples from the other areas; already, in relation to the shoot dry matter, no significant difference among the treatments was observed. The soil properties with the greatest influence on the microbial communities were Al3+ content, considered as high in the Atlantic Forest and neotropical savanna vegetation, as intermediate in the iron outcrops, and as very low in the rehabilitated area revegetated with grass; organic matter, considered as very high in the ironstone outcrops and neotropical savanna, as high in the Atlantic Forest, and as low in the rehabilitated area revegetated with grass; and the pH, with intermediate acidity level in the rehabilitated area revegetated with grass, high level of acidity in the iron outcrops and neotropical savanna, and very high acidity in the Atlantic Forest. After isolation of the nodules, 380 bacterial strains were obtained and separated into 27 groups by cultural characterization analysis. Genetic diversity was evaluated by the 16S rRNA gene partial sequencing of 156 strains, which identified some bacteria belonging to nitrogen-fixing Leguminosae nodulating bacterial genera (Rhizobium, Bradyrhizobium, Burkholderia, and Cupriavidus), some representative of associative bacteria (Bacillus, Paenibacillus, Herbaspirillum, Pseudomonas, and Agrobacterium), and other genera (Brevibacillus, Novosphingobium, Chitinophaga, Dyella, Acinetobacter, and Stenotrophomonas). The highest genetic diversity of bacteria was found in the rehabilitated area revegetated with grass indicated that it was effective in soil rehabilitation</p></div

Bradyrhizobium forestalis sp. nov., an efficient nitrogen-fixing bacterium isolated from nodules of forest legume species in the Amazon

Three strains of nitrogen-fixing bacteria isolated from nodules of Inga sp. (INPA54B(T)) and Swartzia sp. (INPA86A and INPA01-91A) in soils under native forest in the Brazilian Amazon were previously identified as belonging to the Bradyrhizobium genus. In this study, these strains were characterized using a polyphasic approach to establish their taxonomic position. The three strains shared more than 99.5% sequence similarity of the 16S rRNA gene with the type strains of five Bradyrhizobium species (B. japonicum USDA 6(T), B. liaoningense LMG 18230(T), B. ottawaense OO99(T), B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T)). However, multilocus sequence analysis of two (recA and glnII) or three (atpD, gyrB, and recA) housekeeping genes indicated that these three strains represent a new Bradyrhizobium species, which is closely related to B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T). DNA-DNA hybridization values between INPA54B(T) and B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T) were only 41.5 and 30.9%, respectively. Phenotypic characterization also allowed the differentiation of the novel species from B. subterraneum 58 2-1(T) and B. yuanmingense LMG 21827(T). In the phylogenetic analysis of the nodC and nifH genes, the three strains showed similar sequences that were divergent from those of type strains of all Bradyrhizobium species. We concluded that these strains represent a novel species, for which the name Bradyrhizobium forestalis is proposed, with INPA54B(T) (= LMG 10044(T)) as type strain. The G+C content in the DNA of INPA54B(T) is 63.7 mol%

Symbiosis of rhizobia with Gliricidia sepium and Clitoria fairchildiana in an Oxisol in the pre-Amazon region of Maranhão State

<div><p>ABSTRACT. Gliricidia (Gliricidia sepium) and sombreiro (Clitoria fairchildiana) have been recommended for agroforestry systems and reforestation of degraded areas due to their fast growth and symbiosis with rhizobia. However, little is known about native populations that nodulate these species. The objective of this study was to evaluate the phenotypic and genetic diversity of nitrogen-fixing bacteria isolated from nodules of gliricidia and sombreiro in alley cropping systems located in the pre-Amazon region of Maranhão State and to confirm their nodulation ability. Nodules were field collected from 20 plants of each species. The isolated strains were characterized morphologically, their 16S rRNA gene was partially sequenced, and their symbiotic ability was authenticated in siratro (Macroptilium atropurpureum). Despite being in the same climate and soil conditions, gliricidia and sombreiro are nodulated by different rhizobia genera, with Rhizobium predominant in gliricidia and Bradyrhizobium in sombreiro. Endophytic strains also colonized nodules in the field. Approximately 60% of Rhizobium strains did not nodulate siratro, whereas all Bradyrhizobium strains did. Native strains isolated from gliricidia nodules had low efficiency, and only four strains isolated from sombreiro nodules were efficient in siratro. These results highlight the importance of symbiotic relationships in the regulation of biological nitrogen fixation.</p></div