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.

Sulfoacidibacillus ferrooxidans, gen. nov., sp. nov., Sulfoacidibacillus thermotolerans, gen. nov., sp. nov., and Ferroacidibacillus organovorans, gen. nov., sp. nov.: Extremely acidophilic chemolitho-heterotrophic Firmicutes.

Ten strains of extremely acidophilic bacteria, isolated from different environments form a distinct monophyletic clade within the phylum Firmicutes. Comparison of complete genomes of the proposed type strains confirm that they comprise two genera (proposed names Sulfoacidibacillus and Ferroacidibacillus), and at least three species (Sulfoacidibacillus ferrooxidans, Sulfoacidibacillus thermotolerans and Ferroacidibacillus organovorans). The bacterial strains share some physiological traits, including catalysing the dissimilatory oxidation and reduction of iron, and in being obligately heterotrophic. Both species of Sulfoacidibacillus are also able to oxidise elemental sulfur and tetrathionate. Both S. ferrooxidans and Ferroacidibacillus spp. are mesophilic, while S. thermotolerans isolates are moderate thermophiles. The isolates display different degrees of acid-tolerance: Ferroacidibacillus spp. are the most acid-sensitive while the type strain of S. ferrooxidans grows at pH 0.9. MK7 was detected as the sole menaquinone present in all three nominated type strains, and their peptidoglycans all contain meso-2,6 diaminopimelic acid type A1γ. The chromosomal DNA of the strains examined contain between 44 and 52 mol% G + C. The nominated type strains of the new species are S. ferrooxidans S0ABT (= DSM 105355T = JCM 33225T); S. thermotolerans Y002T (= ATCC TSD-104T = JCM 31946T); F. organovorans SLC66T (= ATCC TSD-103T = JCM 31945T).

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.

Isolation and characterization of a novel acidophilic zero-valent sulfur- and ferric iron-respiring Firmicute.

A novel, obligately anaerobic, acidophilic bacterium (strain I2511), isolated from sediment in an abandoned copper mine, was shown to couple the oxidation of organic electron donors to the reduction of both zero-valent sulfur and ferric iron in acidic media. The isolate was an obligate heterotroph that used a variety of organic compounds as electron donors and required yeast extract for growth. Alternative electron acceptors (sulfate, tetrathionate, thiosulfate and nitrate) were not used by the novel isolate. The strain grew as motile, endospore-forming rods, and was mesophilic and moderately acidophilic, with a growth rate of 0.01 h-1 at optimum pH (3.7) and temperature (35 °C). Analysis of its 16S rRNA gene sequence placed strain I2511 within the phylum Firmicutes, distantly related to validated species. Phylogenetic analysis and physiological traits indicate that the novel strain represents a species of a candidate novel genus. Strain I2511 was included in a microbial consortium in a low pH "hybrid" sulfidogenic bioreactor designed to remove chalcophilic metals from metal-contaminated liquors and was present in >50% relative abundance when bioreactor was operated at pH ∼ 2.0. Results indicate that the novel isolate could be applied in biotechnologies to treat acidic and neutral pH, metal-rich effluents.

Draft Genome Sequence of a Novel Acidophilic Iron-Oxidizing Firmicutes Species, "Acidibacillus ferrooxidans" (SLC66T).

Here, we present the draft genome sequence of the type strain of "Acidibacillus ferrooxidans," a mesophilic, heterotrophic, and acidophilic bacterium that was isolated from mine spoilage subjected to accelerated weathering in humidity cell tests carried out by the former U.S. Bureau of Mines in Salt Lake City, UT.

Isolation and characterisation of mineral-oxidising "Acidibacillus" spp. from mine sites and geothermal environments in different global locations.

Eight strains of acidophilic bacteria, isolated from mine-impacted and geothermal sites from different parts of the world, were shown to form a distinct clade (proposed genus "Acidibacillus") within the phylum Firmicutes, well separated from the acidophilic genera Sulfobacillus and Alicyclobacillus. Two of the strains (both isolated from sites in Yellowstone National Park, USA) were moderate thermophiles that oxidised both ferrous iron and elemental sulphur, while the other six were mesophiles that also oxidised ferrous iron, but not sulphur. All eight isolates reduced ferric iron to varying degrees. The two groups shared <95% similarity of their 16S rRNA genes and were therefore considered to be distinct species: "Acidibacillus sulfuroxidans" (moderately thermophilic isolates) and "Acidibacillus ferrooxidans" (mesophilic isolates). Both species were obligate heterotrophs; none of the eight strains grew in the absence of organic carbon. "Acidibacillus" spp. were generally highly tolerant of elevated concentrations of cationic transition metals, though "A. sulfuroxidans" strains were more sensitive to some (e.g. nickel and zinc) than those of "A. ferrooxidans". Initial annotation of the genomes of two strains of "A. ferrooxidans" revealed the presence of genes (cbbL) involved in the RuBisCO pathway for CO2 assimilation and iron oxidation (rus), though with relatively low sequence identities.

Draft Genome Sequence of "Acidibacillus ferrooxidans" ITV01, a Novel Acidophilic Firmicute Isolated from a Chalcopyrite Mine Drainage Site in Brazil.

Here, we report the draft genome sequence of "Acidibacillus ferrooxidans" strain ITV01, a ferrous iron- and sulfide-mineral-oxidizing, obligate heterotrophic, and acidophilic bacterium affiliated with the phylum Firmicutes. Strain ITV01 was isolated from neutral drainage from a low-grade chalcopyrite from a mine in northern Brazil.