Speleothems in quartz-sandstone caves of Ponta Grossa municipality, Campos Gerais region, Paraná state, southern Brazil

The present communication characterizes and discusses the genesis of cave speleothems developed in Furnas Formation (Silurian-Devonian) and Vila Velha sub-unit (Campo Mourão Formation, Upper Carboniferous) quartz-sandstones, in southern Brazil. The research, which involved stratigraphic and petrographic studies, was conducted to identify the faciological context of occurrence of these features, and to determine, through different analytical methods, their mineralogical composition and porosity, and also the action of microbial markers on the genesis of these secondary mineral deposits. The speleothems were classified into six types based on form, composition and genesis: (1) arborescent (coral), (2) mushroom-shaped, (3) stalactitic, (4) stalagmitic, (5) columnar with horizontal/ascending growth, and (6) fibrous. In response to substrate permoporosity, speleothems develop on all sandstone facies of the study area, mainly in sites controlled by bedding, stratification and fracturing planes. They are less frequent, however, in conglomerate and silty-clayey layers of the Furnas Formation, being composed mainly of silica (opal-A and cryptocrystalline silica) and kaolinite, with lesser contribution of gypsum and amorphous iron oxides associated with goethite and hematite. Detritic minerals such as quartz and muscovite also take part in the composition of these features. Plant and invertebrate fragments were identified, including biosignatures and microorganisms capable of favoring precipitation of silica (possibly cyanobacteria and diatom) and iron oxide (possibly Gallionella ferruginea). Such biosignatures and extracellular polymeric substances (biofilms) associated with speleothems are evidence of organomineralization, also known as biologically induced mineralization. The results, which indicate biological action on the genesis of speleothems, raise further discussion on the influence of microorganisms on the dissolution and precipitation of silica and kaolinite in the region.

Structural and Spatial Associations between Fe, O, and C in the Network Structure of the Leptothrix ochracea Sheath Surface

ABSTRACTThe structural and spatial associations of Fe with O and C in the outer coat fibers of theLeptothrix ochraceasheath were shown to be substantially similar to the stalk fibers ofGallionella ferruginea, i.e., a central C core, probably of bacterial origin, and aquatic Fe interacting with O at the surface of the core.

Nanometer-Scale Visualization and Structural Analysis of the Inorganic/Organic Hybrid Structure of Gallionella ferruginea Twisted Stalks

ABSTRACTThe so-called Fe/Mn-oxidizing bacteria have long been recognized for their potential to form extracellular iron hydroxide or manganese oxide structures in aquatic environments. Bacterial species belonging to the genusGallionella, one type of such bacteria, oxidize iron and produce uniquely twisted extracellular stalks consisting of iron oxide-encrusted inorganic/organic fibers. This paper describes the ultrastructure ofGallionellacells and stalks and the visualized structural and spatial localization of constitutive elements within the stalks. Electron microscopy with energy-dispersive X-ray microanalysis showed the export site of the stalk fibers from the cell and the uniform distribution of iron, silicon, and phosphorous in the stalks. Electron energy-loss spectroscopy revealed that the stalk fibers had a central carbon core of bacterial exopolymers and that aquatic iron interacted with oxygen at the surface of the carbon core, resulting in deposition of iron oxides at the surface. This new knowledge of the structural and spatial associations of iron with oxygen and carbon provides deeper insights into the unique inorganic/organic hybrid structure of the stalks.

Diversity of Microorganisms in Fe-As-Rich Acid Mine Drainage Waters of Carnoulès, France

ABSTRACT The acid waters (pH 2.7 to 3.4) originating from the Carnoulès mine tailings contain high concentrations of dissolved arsenic (80 to 350 mg · liter−1), iron (750 to 2,700 mg · liter−1), and sulfate (2,000 to 7,500 mg · liter−1). During the first 30 m of downflow in Reigous creek issuing from the mine tailings, 20 to 60% of the dissolved arsenic is removed by coprecipitation with Fe(III). The microbial communities along the creek have been characterized using terminal-restriction fragment length polymorphism (T-RFLP) and 16S rRNA gene library analyses. The results indicate a low bacterial diversity in comparison with unpolluted water. Eighty percent of the sequences obtained are related to sequences from uncultured, newly described organisms or recently associated with acid mine drainage. As expected owing to the water chemistry, the sequences recovered are mainly related to bacteria involved in the geochemical Fe and S cycles. Among them, sequences related to uncultured TrefC4 affiliated with Gallionella ferruginea, a neutrophilic Fe-oxidizing bacterium, are dominant. The description of the bacterial community structure and its dynamics lead to a better understanding of the natural remediation processes occurring at this site.