Fatima Maria de Souza Moreira

Changes in land use alter the structure of bacterial communities in Western Amazon soils

Here we show how agricultural practices by indigenous peoples as well as forest recovery relate to the structure and composition of Amazon soil bacterial communities. Soil samples were collected in different land use systems and bacterial community composition and diversity were explored by T-RFLP, cloning and sequencing, and data were analyzed with multivariate techniques. The main differences in bacterial community structure were related to changes in the soil attributes that, in turn, were correlated to land use. Community structure changed significantly along gradients of base saturation, [Al3+] and pH. The relationship with soil attributes accounted for about 31% of the variation of the studied communities. Clear differences were observed in community composition as shown by the differential distribution of Proteobacteria, Bacteroidetes, Firmicutes, Acidobacteria and Actinobacteria. Similarity between primary and secondary forest communities indicates the recovery of bacterial community structure during succession. Pasture and crop soil communities were among the most diverse, showing that these land use types did not deplete bacterial diversity under the conditions found in our sites.

Characterization of Rhizobia Isolated from Different Divergence Groups of Tropical Leguminosae by Comparative Polyacrylamide Gel Electrophoresis of their Total Proteins

Summary In an attempt to determine the taxonomic position of and the relationships between some 800 strains of bradyrhizobia and rhizobia isolated from nodules of tropical leguminous plants in the Amazon region and Atlantic forests of Brazil, 171 strains (of which 120 were slow or very slow growers) were selected for study by sodium dodecyl sulphate polyacrylamide gel electrophoresis of proteins (SDS-PAGE). The strains were chosen to represent culturally different isolates from different divergence groups of Leguminosae. Appropriate type and reference strains and also seven tropical strains isolated from Phaseolus vulgaris were included for comparison. At a mean correlation coefficient (r) of 0.86, 23 protein electrophoretic clusters were obtained. The majority of the isolates grouped in a large cluster that contained the type strain of Bradyrhizobium japonicum. This cluster could be divided in 5 subclusters that correlated only to some degree with previously determined DNA homology groups. A few of the isolates could be equated with the species Rhizobium fredii (syn. Sinorhizobium fredii), R. galegae and R. loti but many could not be allocated to currently described taxa. No correlation was noted between clusters obtained and the divergence groups of Leguminosae from which the strains were isolated.

A social and ecological assessment of tropical land uses at multiple scales: the Sustainable Amazon Network

Science has a critical role to play in guiding more sustainable development trajectories. Here, we present the Sustainable Amazon Network (Rede Amazônia Sustentável, RAS): a multidisciplinary research initiative involving more than 30 partner organizations working to assess both social and ecological dimensions of land-use sustainability in eastern Brazilian Amazonia. The research approach adopted by RAS offers three advantages for addressing land-use sustainability problems: (i) the collection of synchronized and co-located ecological and socioeconomic data across broad gradients of past and present human use; (ii) a nested sampling design to aid comparison of ecological and socioeconomic conditions associated with different land uses across local, landscape and regional scales; and (iii) a strong engagement with a wide variety of actors and non-research institutions. Here, we elaborate on these key features, and identify the ways in which RAS can help in highlighting those problems in most urgent need of attention, and in guiding improvements in land-use sustainability in Amazonia and elsewhere in the tropics. We also discuss some of the practical lessons, limitations and realities faced during the development of the RAS initiative so far.

Nodulation of Sesbania species by Rhizobium (Agrobacterium) strain IRBG74 and other rhizobia.

Summary Concatenated sequence analysis with 16S rRNA, rpoB and fusA genes identified a bacterial strain (IRBG74) isolated from root nodules of the aquatic legume Sesbania cannabina as a close relative of the plant pathogen Rhizobium radiobacter (syn. Agrobacterium tumefaciens). However, DNA:DNA hybridization with R. radiobacter, R. rubi, R. vitis and R. huautlense gave only 44%, 5%, 8% and 8% similarity respectively, suggesting that IRBG74 is potentially a new species. Additionally, it contained no vir genes and lacked tumour‐forming ability, but harboured a sym‐plasmid containing nifH and nodA genes similar to those in other Sesbania symbionts. Indeed, IRBG74 effectively nodulated S. cannabina and seven other Sesbania spp. that nodulate with Ensifer (Sinorhizobium)/Rhizobium strains with similar nodA genes to IRBG74, but not species that nodulate with Azorhizobium or Mesorhizobium. Light and electron microscopy revealed that IRBG74 infected Sesbania spp. via lateral root junctions under flooded conditions, but via root hairs under non‐flooded conditions. Thus, IRBG74 is the first confirmed legume‐nodulating symbiont from the Rhizobium (Agrobacterium) clade. Cross‐inoculation studies with various Sesbania symbionts showed that S. cannabina could form fully effective symbioses with strains in the genera Rhizobium and Ensifer, only ineffective ones with Azorhizobium strains, and either partially effective (Mesorhizobium huakii) or ineffective (Mesorhizobium plurifarium) symbioses with Mesorhizobium. These data are discussed in terms of the molecular phylogeny of Sesbania and its symbionts.

Genetic and symbiotic diversity of nitrogen-fixing bacteria isolated from agricultural soils in the western Amazon by using cowpea as the trap plant.

ABSTRACT Cowpea is a legume of great agronomic importance that establishes symbiotic relationships with nitrogen-fixing bacteria. However, little is known about the genetic and symbiotic diversity of these bacteria in distinct ecosystems. Our study evaluated the genetic diversity and symbiotic efficiencies of 119 bacterial strains isolated from agriculture soils in the western Amazon using cowpea as a trap plant. These strains were clustered into 11 cultural groups according to growth rate and pH. The 57 nonnodulating strains were predominantly fast growing and acidifying, indicating a high incidence of endophytic strains in the nodules. The other 62 strains, authenticated as nodulating bacteria, exhibited various symbiotic efficiencies, with 68% of strains promoting a significant increase in shoot dry matter of cowpea compared with the control with no inoculation and low levels of mineral nitrogen. Fifty genotypes with 70% similarity and 21 genotypes with 30% similarity were obtained through repetitive DNA sequence (BOX element)-based PCR (BOX-PCR) clustering. The 16S rRNA gene sequencing of strains representative of BOX-PCR clusters showed a predominance of bacteria from the genus Bradyrhizobium but with high species diversity. Rhizobium, Burkholderia, and Achromobacter species were also identified. These results support observations of cowpea promiscuity and demonstrate the high symbiotic and genetic diversity of rhizobia species in areas under cultivation in the western Amazon.

Efeitos do glifosato sobre microrganismos simbiotróficos de soja, em meio de cultura e casa de vegetação

The effects of the Roundup herbicide on three strains of Bradyrhizobium elkanii (BR 29, INPA 80A and INPA 553A), one of B. japonicum (BR 86), and on three species of arbuscular mycorrhizal fungi (AMF) (Gigaspora margarita,Glomus etunicatum and Scutellospora heterogama), were evaluated in culture media containing increasing concentrations of the herbicide (0_454 µM); evaluations were also made on the effects on nodulation and mycorrhiza colonization of soybean grown in a soil treated with Roundup doses equivalent to 1.25 to 10 L ha-1 before sowing. The herbicide inhibited growth of Bradyrhizobium spp. and AMF in culture medium. These effects were directly related to increasing concentrations, and varied depending on the strain and species evaluated. However, in vitro inhibition occurred only when concentrations were greater than that recommended for use in the field. Strains BR 29, INPA 553A and INPA 80A showed to be more resistant to glyphosate, when compared to BR 86. Herbicide inhibition on germination and growth of AMF spore germ tubes decreased from G. etunicatum to S. heterogama and G. margarita. Soil application of Roundup before sowing up to a dose equivalent to 10 L ha-1 had no effect on nodulation and mycorrhiza colonization of soybean.

Nitrogen-fixing bacteria communities occurring in soils under different uses in the Western Amazon Region as indicated by nodulation of siratro (Macroptilium atropurpureum)

Understanding native communities is a crucial step for the management of biological nitrogen fixation, since they may be either a source of efficient strains or a limiting factor when efficient strains need to be introduced. This work aimed to evaluate the density, diversity and efficiency of Leguminosae nodulating bacterial (LNB) communities and their component strains in soils under various land use systems (LUSs): pristine forest, agriculture, pasture, agroforestry, young secondary forest, and old secondary forest,. The LNB communities were trapped from these soils by using the promiscuous host siratro under controlled conditions. We also studied their relationships with physical and chemical attributes of the soil. Agroforestry and agriculture soil samples induced the highest number of nodules in siratro, while forest soil samples induced the lowest number of nodules. No relationship was found between LNB and Leguminosae species diversity in the LUSs. The soil chemical variables that were most related to differences in nodule number and shoot dry matter weight of plants inoculated with soil suspensions of the LUSs were, respectively: Ca2+, Mg2+, base saturation, exchangeable bases and Cu2+; and pH, cation exchange capacity, B, Cu2+ and clay. Although, LNB communities from all LUSs were efficient under controlled and similar conditions, they were found to be composed of strains with variable efficiency: inefficient, efficient, highly efficient and superior efficiency. Efficient strains occurred at the highest frequency in all LUSs. The isolated strains presented similar and new sequences that were phylogenetically related to well known LNB genera in α-and β-Proteobacteria. Unusual genera in these branches, as well as in other branches, which are probably endophytic bacteria, were also isolated from nodules. These data support siratro as a useful trap species to study the LNB biodiversity of diverse ecosystems in tropical soils. The fact that the highest diversity and nodulation were seen in managed systems such as agriculture and agroforestry suggests a high resilience of LNB communities to changes in land use after deforestation in a region where large forest areas are still preserved and can be a source of propagules.

Biological nitrogen fixation and phosphate solubilization by bacteria isolated from tropical soils

IntroductionIn addition to fixing atmospheric nitrogen, some bacterial isolates can also solubilize insoluble phosphates, further contributing to plant growth.AimsThe objectives of this study were the following: isolate, select, and identify nodulating bacteria in the cowpea that are efficient not only in biological nitrogen fixation (BNF) but also in the solubilization of insoluble inorganic phosphates; identify and quantify the organic acids produced; and establish the relationship between those acids and the solubilizing capacity.MethodsThe bacteria were captured from two soils containing high concentrations of insoluble phosphorus from the cities of Lavras and Patos de Minas, using the cowpea [Vigna unguiculata (L.) Walp.] as bait. We obtained 78 strains, which were characterized according to their cultural attributes in culture medium 79 with the strains UFLA 03-84, INPA 03-11B, and BR3267 (approved by the Ministry of Livestock and Supply Agriculture—MAPA, as inoculants for the cowpea) and Burkholderia cepacia (LMG1222T), which was used as a positive control for phosphate solubilization. Strains that were selected for their efficiency in both processes were identified by 16S rDNA sequence analysis. We evaluated the symbiotic efficiency (BNF) in a greenhouse and the solubilization efficiency of CaHPO4, Al(H2PO4)3, and FePO4.2H2O in solid and liquid GELP media. Strains that excelled at the solubilization of these phosphate sources were also evaluated for the production of the following organic acids: oxalic, citric, gluconic, lactic, succinic, and propionic.ResultsThe presence of Acinetobacter, Bacillus, Firmicutes, Microbacterium, Paenibacillus, and Rhizobium was detected by 16S rDNA sequencing and analysis. Bacterial strains obtained from cowpea nodules varied greatly in the efficiency of their BNF and phosphate solubilization processes, especially in the strains UFLA 03-09, UFLA 03-10, UFLA 03-12, and UFLA 03-13, which were more efficient in both processes. More strains were able to solubilize insoluble inorganic calcium and iron phosphates in liquid medium than in solid medium. The production of organic acids was related to the solubilization of CaHPO4 and FePO4.2H2O for some strains, and the type and concentration of the acid influenced this process.ConclusionsThese are the first results obtained with bacterial isolates from tropical soils in which the production of organic acids was detected and quantified to examine the solubilization of insoluble inorganic phosphates.

Avaliação agronômica de um biossólido industrial para a cultura do milho

The objective of this work was to evaluate the agronomic feasibility of an industrial biosolid for corn. The experiment was carried out on a dystrophic Cambisol in two cropping seasons, 1999/2000 and 2000/2001. The application of 0, 6, 12, 18 and 24 Mg ha-1 of biosolid dry matter basis, supplemented with K2O in both trials and with 1/3 of the recommended P2O5 rate in the second trial was compared to the complete mineral fertilization. Biosolid application enhanced soil fertility, crop nutrition and grain productivity. Yield response to doses was quadratic, and reached the maximum of 9,992 kg ha-1 with 22.5 Mg ha-1 of biosolid, 21% higher than the complete mineral fertilization and 74% higher than the control with no fertilizer added. Even in the largest biosolid dose, no symptom of nutrients, sodium or heavy metals toxicity was found. The equivalence in productivity to the mineral fertilization (7,895 kg ha-1) was attained with 10 Mg ha-1 of biosolid. Based on this equivalence to NPK, the biosolid fertilizer value was estimated in R

Crescimento e teor de metais de mudas de espécies arbóreas cultivadas em solo contaminado com metais pesados

43.70 per Mg for dry residue and in R