Evolution of biofilms during the colonization process of pyrite by Acidithiobacillus thiooxidans |
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Authors: | Dulce M González René H Lara Keila N Alvarado Donato Valdez-Pérez Hugo R Navarro-Contreras Roel Cruz Jessica Viridiana García-Meza |
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Institution: | (1) Geomicrobiology, Institute of Metallurgy, UASLP, Sierra Leona 550, Lomas 2?, 78210 San Luis Potos?, SLP, Mexico;(2) Basics Sciences Laboratory, UASLP, Salvador Nava 110, 78210 SLP, Mexico;(3) Institute of Physics, UASLP, Salvador Nava 110, 78210 SLP, Mexico;(4) CIACyT, UASLP, Sierra Leona 550, Lomas 2?, 78210 SLP, Mexico; |
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Abstract: | We have applied epifluorescence principles, atomic force microscopy, and Raman studies to the analysis of the colonization
process of pyrite (FeS2) by sulfuroxidizing bacteria Acidithiobacillus thiooxidans after 1, 15, 24, and 72 h. For the stages examined, we present results comprising the evolution of biofilms, speciation of
Sn2−/S0 species, adhesion forces of attached cells, production and secretion of extracellular polymeric substances (EPS), and its
biochemical composition. After 1 h, highly dispersed attached cells in the surface of the mineral were observed. The results
suggest initial non-covalent, weak interactions (e.g., van der Waal’s, hydrophobic interactions), mediating an irreversible
binding mechanism to electrooxidized massive pyrite electrode (eMPE), wherein the initial production of EPS by individual
cells is determinant. The mineral surface reached its maximum cell cover between 15 to 24 h. Longer biooxidation times resulted
in the progressive biofilm reduction on the mineral surface. Quantification of attached cell adhesion forces indicated a strong
initial mechanism (8.4 nN), whereas subsequent stages of mineral colonization indicated stability of biofilms and of the adhesion
force to an average of 4.2 nN. A variable EPS (polysaccharides, lipids, and proteins) secretion at all stages was found; thus,
different architectural conformation of the biofilms was observed during 120 h. The main EPS produced were lipopolysaccharides
which may increase the hydrophobicity of A. thiooxidans biofilms. The highest amount of lipopolysaccharides occurred between 15–72 h. In contrast with abiotic surfaces, the progressive
depletion of Sn2−/S0 was observed on biotic eMPE surfaces, indicating consumption of surface sulfur species. All observations indicated a dynamic
biooxidation mechanism of pyrite by A. thiooxidans, where the biofilms stability and composition seems to occur independently from surface sulfur species depletion. |
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