Enhancing iron biogeochemical cycling for canga ecosystem restoration: insights from microbial stimuli.

Introduction: The microbial-induced restoration of ferruginous crusts (canga), which partially cover iron deposits and host unique ecosystems, is a promising alternative for reducing the environmental impacts of the iron mining industry. Methods: To investigate the potential of microbial action to accelerate the reduction and oxidation of iron in substrates rich in hematite and goethite, four different microbial treatments (water only as a control - W; culture medium only - MO; medium + microbial consortium - MI; medium + microbial consortium + soluble iron - MIC) were periodically applied to induce iron dissolution and subsequent precipitation. Except for W, all the treatments resulted in the formation of biocemented blocks. Results: MO and MI treatments resulted in significant goethite dissolution, followed by precipitation of iron oxyhydroxides and an iron sulfate phase, due to iron oxidation, in addition to the preservation of microfossils. In the MIC treatment, biofilms were identified, but with few mineralogical changes in the iron-rich particles, indicating less iron cycling compared to the MO or MI treatment. Regarding microbial diversity, iron-reducing families, such as Enterobacteriaceae, were found in all microbially treated substrates. Discussion: However, the presence of Bacillaceae indicates the importance of fermentative bacteria in accelerating the dissolution of iron minerals. The acceleration of iron cycling was also promoted by microorganisms that couple nitrate reduction with Fe(II) oxidation. These findings demonstrate a sustainable and streamlined opportunity for restoration in mining areas.

Environmental and agronomic assessment of soil conditioners produced from bauxite residue and oil palm wastes.

Soil conditioner is class of products used to enhance physics, physicochemical or soil biological activities, being able to recover disturbed or nutritional unbalanced soils. The formulation of a soil conditioner composed by bauxite residue (BR), and organic oil palm wastes, as raw materials, was recently proposed as an innovative strategy for the Brazilian acid soils amendment. Here we show the results of soil conditioner amended soil leaching tests and agronomical performance. The soil conditioners were formulated by BR mixed with decomposed POC (palm oil compost) and non-decomposed POMW (palm oil mill waste) oil palm wastes, in the proportion of 25% BR + 75% POC (T1) and 50% BR + 50% POMW (T2), in addition to the treatment with 100% POMW without BR (T3) and limestone at a dose calculated to raise soil pH to 6.0 (T4). Except for T4, all conditioners were applied to the soil at doses of 40, 80, and 120 t ha-1 for leaching tests. The experimental plots were composed of polyvinyl chloride columns, filled with 5 kg of soil, with bottles adapted with hoses at the bottom to facilitate drainage of the leachate. After leaching tests, the respective columns were used as pots for the cultivation of Brachiaria grass, stage with addition of a control composed by undisturbed soil (T5). The pH of the leachates had changes, but the use of BR associated with POMW was similar to the use of limestone. Of the 65 chemical elements evaluated, only nine were identified in the leachate, being most of them considered as plant nutrients. As for soil pH, limestone was slightly higher (6.6) than treatments that had BR (5.5). Brachiaria grass cultivated in the soil amended with conditioners showed similar results of limestone treated soil for the parameters of plant development and showed fertility improvement.

Comparison of two acidophilic sulfidogenic consortia for the treatment of acidic mine water.

Sulfate-reducing bioreactors are a biotechnological alternative for the treatment of acid mine drainage (AMD). In this study, two separate bioreactors with pH and temperature-controlled (Bio I and II) were operated with two different acidophilic microbial consortia to determine their efficiencies in sulfate removal from a synthetic acidic mine water. The bioreactors were operated for 302 days in continuous flow mode under the same parameters: fed with a sulfate solution of ∼30 mM with a pH of 2.5, the temperature at 30°C, stirred gently at 40 rpm and using a continuous stream of nitrogen to help remove the H2S produced in the bioreactor. The glycerol consumption, acetate production, and sulfate removal were monitored throughout the course of the experiment. The community composition and potential metabolic functional groups were analyzed via 16S rRNA partial gene sequencing. Bio I consortium reduced the sulfate, achieving a range of sulfate concentration from 4.7 to 19 mM in the effluent liquor. The removal of sulfate in Bio II was between 5.6 and 18 mM. Both bioreactors' communities showed the presence of the genus De sulfosporosinus as the main sulfate-reducing bacteria (SRB). Despite differences in microbial composition, both bioreactors have similar potential metabolism, with a higher percentage of microorganisms that can use sulfate in respiration. Overall, both bioreactors showed similar performance in treating acidic mine water containing mostly sulfate using two different acidophilic sulfidogenic consortia obtained from different global locations.

Bauxite residue valorization - Soil conditioners production through composting with palm oil mill residual biomass.

Bauxite residue (BR) is a by-product of Bayer process, which is applied for alumina production. Due to its inherent alkalinity and sodicity, the use of BR is globally limited to 23% of the 150 million tons (Mt) produced annually. Maximizing alternative and large-scale uses of BR is a game changer to promote the sustainability of the aluminum production chain. As a strategy for BR valorization, a soil conditioner composed of BR and palm oil residual biomass was proposed. Here we evaluate the BR (25%, 50% and 75%) batch composting with raw palm oil mill waste (POMW) and palm oil compost (POC). The pH, EC, total N and organic carbon, C:N ratio, water holding capacity (WHC), cation exchange capacity (CEC), granulometry and elemental composition were determined after 90 days of composting. Changes in temperature, pH and EC curves were observed during composting of soil conditioners for 90 days. Composting reduced the alkalinity and sodicity of BR, increasing CEC, moisture, organic carbon and total nitrogen. The formulation containing 25% of BR and 75% of POC showed WHC ≥ 60% and CEC ≥ 200 mmolc·kg-1, meeting the Brazilian legislation for production and commercialization of soil conditioners. This strategy could potentially consume 7.6% of all BR produced annually in the largest Brazilian alumina refinery. Concentrations of potentially toxic elements were far below the allowable levels in all formulations. Major and minor plant nutrients were present and the composting aggregated small particles in BR. Composting of BR is a new alternative for the valorization of mining tailings, allowing the development of an environmentally friendly and zero-waste product, which can be applied on a large scale in agriculture to improve soil fertility.

Fungal Community Assembly in the Amazonian Dark Earth.

Here, we compare the fungal community composition and diversity in Amazonian Dark Earth (ADE) and the respective non-anthropogenic origin adjacent (ADJ) soils from four different sites in Brazilian Central Amazon using pyrosequencing of 18S ribosomal RNA (rRNA) gene. Fungal community composition in ADE soils were more similar to each other than their ADJ soils, except for only one site. Phosphorus and aluminum saturation were the main soil chemical factors contributing to ADE and ADJ fungal community dissimilarities. Differences in fungal richness were not observed between ADE and ADJ soil pairs regarding to the most sites. In general, the most dominant subphyla present in the soils were Pezizomycotina, Agaricomycotina, and Mortierellomycotina. The most abundant operational taxonomic units (OTUs) in ADE showed similarities with the entomopathogenic fungus Cordyceps confragosa and the saprobes Fomitopsis pinicola, Acremonium vitellinum, and Mortierellaceae sp., whereas OTUs similar to Aspergillus niger, Lithothelium septemseptatum, Heliocephala gracillis, and Pestalosphaeria sp. were more abundant in ADJ soils. Differences in fungal community composition were associated to soil chemical factors in ADE (P, Ca, Zn, Mg, organic matter, sum of bases, and base saturation) and ADJ (Al, potential acidity, Al saturation, B, and Fe) soils. These results contribute to a deeper view of the fungi communities in ADE and open new perspectives for entomopathogenic fungi studies.

CitEST libraries

In order to obtain a better understanding of what is citrus, 33 cDNA libraries were constructed from different citrus species and genera. Total RNA was extracted from fruits, leaves, flowers, bark, seeds and roots, and subjected or not to different biotic and abiotic stresses (pathogens and drought) and at several developmental stages. To identify putative promoter sequences, as well as molecular markers that could be useful for breeding programs, one shotgun library was prepared from sweet orange (Citrus sinensis var. Olimpia). In addition, EST libraries were also constructed for a citrus pathogen, the oomycete Phythophthora parasitica in either virulent or avirulent form. A total of 286,559 cDNA clones from citrus were sequenced from their 5’ end, generating 242,790 valid reads of citrus. A total of 9,504 sequences were produced in the shotgun library and the valid reads were assembled using CAP3. In this procedure, we obtained 1,131 contigs and 4,083 singletons. A total of 19,200 cDNA clones from P. parasitica were sequenced, resulting in 16,400 valid reads. The number of ESTs generated in this project is, to our knowledge, the largest citrus sequence database in the world.