INFLUENCE OF ACIDOPHILIC MICROORGANISMS IN THE GEOCHEMISTRY OF THE AMARILLO RIVER

DONATI, E.; MAZA, S.N.; COLLO, G.; LECOMTE K.L.; ASTINI, R.A.; BERNARDELLI C

Congreso; XIII Congreso Argentino De Microbiología General ? SAMIGE; 2018

The Amarillo River is located on the eastern slope of the Sierra de Famatina (La Rioja, Argentina) in `Nevados de Famatina´ mining district where La Mejicana mine operated between 1890 and 1925. This fluvial system drains headwaters through a zone of alteration, an important halo of high-sulfidation epithermal deposits (Au?Cu?Ag?As?Sb?Te) and Cu and Mo porphyries. The river is characterized by sulfated acidic waters (pH ~ 3) of reddish-yellow colorations with high concentrations of dissolved total solids and metals. This high concentration of metals and acidity is generally associated with high rates of oxidation and leaching of pyrite and other sulfide minerals due to natural exposure or mining activity. Along the river a widespread deposition of ochreous sediments associated with the precipitation of Fe(III) compounds can be observed. Jarosite (XFe3(SO4)2(OH)6) is the main precipitated phase in upper riverbed, while schwertmannite (Fe8O8(OH)6(SO4).nH2O) dominates the middle and lower ones. In this work, we establish the role of the microorganisms present in Amarillo River on the oxidation of Fe(II) and the subsequent precipitation of different hydroxysulfates. Consortia were obtained from the enrichment of samples coming from the upper and middle basins of the Amarillo River using culture medium Mac pH 1.8-Fe(II) 9 g.L-1 with yeast extract 2 g.L-1 (heterotrophic consortium) and without yeast extract (autotrophic consortium). Biotic oxidation of Fe(II) was confirmed by comparison with abiotic controls. DNA was extracted and bacterial ribosomal RNA genes were amplified, cloned, and sequenced. Iron-oxidizing bacteria and other acidophiles associated to them were detected and isolated. Moreover, yeasts and fungi were also isolated by culture in solid medium from the heterotrophic consortia. To recreate the natural biomineral formation in-vitro laboratory study was carried out: inocula from each consortium was inoculated in 9K medium pH 2.0; abiotic controls replacing the inoculum by fresh medium were also done. After 28 days, the precipitates were harvested, washed, dried at 60 °C, and analyzed by X-ray diffraction (XRD). Two different patterns were obtained: one for biotic precipitates with well-defined and intense peaks suggesting well-crystallized phases belonging to the jarosite group and a second for abiotic controls with broad peaks that indicate low crystalline phases possibly related to schwertmannite precursors. Besides, the morphology of the precipitates was investigated with scanning electron microscopy (SEM) detecting cells and nano-sized precipitates which were covering the cell surface. Mineral aggregates had similarity with synthetic jarosites. These results suggest that the geochemical processes of Amarillo River should be interpreted including the activity of the native microorganisms.