Manganese oxide biominerals from freshwater environments in Quadrilatero Ferrifero, Minas Gerais, Brazil.

Biogeochemical Mn cycling in aquatic environments is driven mostly by microbes, and includes reductive dissolution in anaerobic sediments as well as oxidation in aerobic regions. Oxidation is followed by precipitation, which occurs mainly on the extracellular structures of microorganisms. In this work, we studied the minerals precipitated on extracellular structures of native microorganisms from freshwater environments in Quadrilatero Ferrifero (Iron Quadrangle), Minas Gerais, Brazil, known to contain high levels of manganese. Light microscopy of biofilms and floating material showed diverse biomineralized structures. The most conspicuous were identified as the holdfasts of algae from the genus Ulothrix. Diatom frustules associated to manganese oxide precipitates were relatively common. In addition, both filaments and holdfasts produced by bacteria of the genus Leptothrix were found, as well as structures similar to those described as Siderocapsa and Metallogenium. Some previously unknown structures were also observed. Transmission electron microscopy of most of these structures showed the ?crumpled tissue-paper? morphology common in biomineralised manganese oxides. Energy-dispersive X-ray analysis (EDXA) showed that manganese and oxygen were the main components, along with minor amounts of Al, P, S, K, Ca and/or Ba. Our results bring new perspectives to the study of biomineralized manganese oxide structures from the environment. Moreover, they add information about the background of present-day microbial structures needed to better interpret fossilized microbial biominerals

Multicellular life cycle of magnetotactic prokaryotes

6 p. : il.Most multicellular organisms, prokaryotes as well as animals, plants and algae have a unicellular stage in their life cycle. Here, we describe an uncultured prokaryotic magnetotactic multicellular organism that reproduces by binary fission. It is multicellular in all the stages of its life cycle, and during most of the life cycle the cells organize into a hollow sphere formed by a functionally coordinated and polarized single-cell layer that grows by increasing the cell size. Subsequently, all the cells divide synchronously; the organism becomes elliptical, and separates into two equal spheres with a torsional movement in the equatorial plane. Unicellular bacteria similar to the cells that compose these organisms have not been found. Molecular biology analysis showed that all the organisms studied belong to a single genetic population phylogenetically related to many-celled magnetotactic prokaryotes in the delta sub-group of the proteobacteria. This appears to be the first report of a multicellular prokaryotic organism that proliferates by dividing into two equal multicellular organisms each similar to the parent one

Dissimilatory Iron-Reducing Microorganisms Are Present and Active in the Sediments of the Doce River and Tributaries Impacted by Iron Mine Tailings from the Collapsed Fundão Dam (Mariana, MG, Brazil)

On 5 November 2015, a large tailing deposit failed in Brazil, releasing an estimated 32.6 to 62 million m3 of iron mining tailings into the environment. Tailings from the Fundão Dam flowed down through the Gualaxo do Norte and Carmo riverbeds and floodplains and reached the Doce River. Since then, bottom sediments have become enriched in Fe(III) oxyhydroxides. Dissimilatory iron-reducing microorganisms (DIRMs) are anaerobes able to couple organic matter oxidation to Fe(III) reduction, producing CO2 and Fe(II), which can precipitate as magnetite (FeO·Fe2O3) and other Fe(II) minerals. In this work, we investigated the presence of DIRMs in affected and non-affected bottom sediments of the Gualaxo do Norte and Doce Rivers. The increase in Fe(II) concentrations in culture media over time indicated the presence of Fe(III)-reducing microorganisms in all sediments tested, which could reduce Fe(III) from both tailings and amorphous ferric oxyhydroxide. Half of our enrichment cultures converted amorphous Fe(III) oxyhydroxide into magnetite, which was characterized by X-ray diffraction, transmission electron microscopy, and magnetic measurements. The conversion of solid Fe(III) phases to soluble Fe(II) and/or magnetite is characteristic of DIRM cultures. The presence of DIRMs in the sediments of the Doce River and tributaries points to the possibility of reductive dissolution of goethite (α-FeOOH) and/or hematite (α-Fe2O3) from sediments, along with the consumption of organics, release of trace elements, and impairment of water quality