How to cite: Castro JL, Souza MG, Rufini M, Guimarães AA, Rodrigues TL, Moreira FMS. Diversity and efficiency of rhizobia communities from iron mining areas using cowpea as a trap plant. Rev Bras Cienc Solo. 2017;41:e0160525. https://doi.org/10.1590/18069657rbcs20160525Copyright: This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided that the original author and source are credited. Division -Soil Processes and Properties 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 Al 3+ 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 identifie...

Three strains of nitrogen-fixing bacteria isolated from nodules of Inga sp. (INPA54B) 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, B. liaoningense LMG 18230, B. ottawaense OO99, B. subterraneum 58 2-1 and B. yuanmingense LMG 21827). 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 and B. yuanmingense LMG 21827. DNA-DNA hybridization values between INPA54B and B. subterraneum 58 2-1 and B. yuanmingense LMG 21827 were only 41.5 and 30.9%, respectively. Phenotypic characterization also allowed the differentiation of the novel species from B. subterraneum 58 2-1 and B. yuanmingense LMG 21827. 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 (= LMG 10044) as type strain. The G+C content in the DNA of INPA54B is 63.7 mol%.

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.Keywords: Bradyrhizobium; Rhizobium; Papilionoideae; tree legumes; acid soil. Simbioses de rizóbios comGliricidia sepium e Clitoria fairchildiana em um Oxisol na região da Pré-Amazônia do Estado do Maranhão RESUMO. Gliricídia (Gliricidia sepium) e sombreiro (Clitoria fairchildiana) têm sido recomendadas para uso em sistemas agroflorestais e reflorestamento de áreas degradadas devido ao seu rápido crescimento e simbiose com rizóbios. No entanto, pouco é conhecido em relação às populações nativas que nodulam estas espécies. O objetivo deste estudo foi avaliar a diversidade genética e fenotípica das bactérias fixadoras de nitrogênio isoladas de nódulos de gliricídia e sombreiro em sistemas alley cropping localizados na região pré-Amazônica do Estado do Maranhão, e autenticar sua capacidade de nodulação. Foram realizados: coleta dos nódulos em campo, isolamento, caracterização cultural, sequenciamento parcial do gene 16S rRNA e autenticação da capacidade simbiótica das estirpes em siratro (Macroptilium atropurpureum). Apesar de estarem sob as mesmas condições edafoclimáticas, gliricídia e sombreiro são colonizados por distintos gêneros de rizóbios, com predominância de Rhizobium em gliricídia, e Bradyrhizobium em sombreiro. Estirpes endofíticas também foram encontradas colonizando os nódulos. Cerca de 60% das estirpes de Rhizobium não nodularam siratro e todas de Bradyrhizobium nodularam esta espécie. Todas as estirpes nativas isoladas de nódulos de gliricídia apresentaram baixa eficiência, e somente quatro de sombreiro foram eficientes em siratro. Estes resultados ressaltam a importância das rela...

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We evaluated symbiotic (rhizobia) and non-symbiotic efficiency and the diversity of native communities of plant growth-promoting rhizobacteria (PGPR) in soil samples from an area in recovery after iron mining (RA) and from adjacent phytophysiognomies (Ironstone Outcrops, Neotropical Savanna, Atlantic Forest) in the Quadrilátero Ferrífero region, MG, Brazil, in two climate seasons. Greenhouse experiments were conducted with siratro (Macroptilium atropurpureum) as a trap plant. The SPAD index in siratro was more effective in detecting the difference between the symbiotic efficiencies of the communities of PGPR than shoot dry matter, with readings of the SPAD index greater in RA. Genetic diversity, of 327 strains evaluated by partial sequencing of the 16S rRNA gene, showed 29 genera in the dry season and 19 in the rainy season, among these genera some recognized as nodulating and endophytes, and others potentially endophytes. Genera belonging to the phyla Acidobacteria, Actinobacteria, Bacteroidetes, Firmicutes, and Proteobacteria were found. The nodule-forming genera Bradyrhizobium and Rhizobium and the endophytic Paenibacillus were those of highest occurrence in both seasons and in all phytophysiognomies. The greater symbiotic efficiency and the high genetic diversity of the rhizobacterial community found in RA indicate that soil rehabilitation is effectively in process. As most of native legume species form symbiosis with Rhizobium and mainly Bradyrhizobium, these bacterial communities are an important source of potential inoculant strains, as well as, a relevant feature for the successful establishment of diverse legumes for revegetation purposes.

Lima bean (Phaseolus lunatus L.) is the second most important species of the Phaseolus genus worldwide. In Brazil, it is grown primarily in the semiarid Northeast region. Although lima bean establishes symbiosis with N 2 -fixing bacteria (rhizobia), there is not yet a recommended inoculant. The aim of this study was to phenotypically and genotypically characterize rhizobia strains isolated from root nodules of lima bean collected in a Northeast region, and to evaluate their efficiency in supplying N nutrition to the crop under axenic conditions and in a Humic Rhodic Hapludox with and without correction of acidity. The symbiotic efficiencies were evaluated in a greenhouse under axenic conditions and, afterward, in pots with nonautoclaved soil with and without liming. Treatments consisted of the strains under evaluation, controls without inoculation (with low or high concentration or without mineral N), and a strain efficient for the crop. In all, 66 strains were isolated from the root nodules with predominance of strains belonging to the Bradyrhizobium genus. Liming brought about increases in lima bean development as it interacted with some strains. Six strains of the Bradyrhizobium genus, belonging to groups of type strains that include B. elkanii and B. japonicum, stood out for their biotechnological potential as inoculants for lima bean, and they should be tested in the field with the aim of validating their recommendation as inoculants for that crop.

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