Metal Mobilization by Iron- and Sulfur-Oxidizing Bacteria in a Multiple Extreme Mine Tailings in the Atacama Desert, Chile

The marine shore sulfidic mine tailings dump at the Chañaral Bay in the Atacama Desert, northern Chile, is characterized by extreme acidity, high salinity, and high heavy metals concentrations. Due to pyrite oxidation, metals (especially copper) are mobilized under acidic conditions and transported toward the tailings surface and precipitate as secondary minerals (Dold, <i>Environ. Sci. Technol</i>. <b>2006</b>, <i>40</i>, 752–758.). Depth profiles of total cell counts in this almost organic-carbon free multiple extreme environment showed variable numbers with up to 10⁸ cells g^–1 dry weight for 50 samples at four sites. Real-time PCR quantification and bacterial 16S rRNA gene diversity analysis via clone libraries revealed a dominance of <i>Bacteria</i> over <i>Archaea</i> and the frequent occurrence of the acidophilic iron­(II)- and sulfur-oxidizing and iron­(III)-reducing genera <i>Acidithiobacillus</i>, <i>Alicyclobacillus</i>, and <i>Sulfobacillus.</i> Acidophilic chemolithoautotrophic iron­(II)-oxidizing bacteria were also frequently found via most-probable-number (MPN) cultivation. Halotolerant iron­(II)-oxidizers in enrichment cultures were active at NaCl concentrations up to 1 M. Maximal microcalorimetrically determined pyrite oxidation rates coincided with maxima of the pyrite content, total cell counts, and MPN of iron­(II)-oxidizers. These findings indicate that microbial pyrite oxidation and metal mobilization preferentially occur in distinct tailings layers at high salinity. Microorganisms for biomining with seawater salt concentrations obviously exist in nature

Acid Rock Drainage and Rock Weathering in Antarctica: Important Sources for Iron Cycling in the Southern Ocean

Here we describe biogeochemical processes that lead to the generation of acid rock drainage (ARD) and rock weathering on the Antarctic landmass and describe why they are important sources of iron into the Antarctic Ocean. During three expeditions, 2009–2011, we examined three sites on the South Shetland Islands in Antarctica. Two of them displayed intensive sulfide mineralization and generated acidic (pH 3.2–4.5), iron-rich drainage waters (up to 1.78 mM Fe), which infiltrated as groundwater (as Fe²⁺) and as superficial runoff (as Fe³⁺) into the sea, the latter with the formation of schwertmannite in the sea-ice. The formation of ARD in the Antarctic was catalyzed by acid mine drainage microorganisms found in cold climates, including <i>Acidithiobacillus ferrivorans</i> and <i>Thiobacillus plumbophilus</i>. The dissolved iron (DFe) flux from rock weathering (nonmineralized control site) was calculated to be 0.45 × 10⁹ g DFe yr^–1 for the nowadays 5468 km of ice-free Antarctic rock coastline which is of the same order of magnitude as glacial or aeolian input to the Southern Ocean. Additionally, the two ARD sites alone liberate 0.026 and 0.057 × 10⁹ g DFe yr^–1 as point sources to the sea. The increased iron input correlates with increased phytoplankton production close to the source. This might even be enhanced in the future by a global warming scenario, and could be a process counterbalancing global warming