Attachment of Leptospirillum sp. to chemically modified pyrite surfaces. Fast and simple electrochemical monitoring of bacterial-mineral interactions

Bacterial cell attachment that results in biofilm formation is the first step of bacteria-mineral interaction, and it is known that they strongly depend on the chemical characteristics of the mineral surface. In some industrial processes, like those used in biohydrometallurgy, the minerals are present in different chemical oxidation states, especially when heterogeneous low-grade ore deposits and mining tailings are used as starting materials for microbial inoculation. This study describes a strategy for monitoring bacterial attachment to pyrite (FeS2) and surface modified pyrite weathered in the culture growth medium used (pH 1.8), by means of a non-invasive electrochemical technique such as electrochemical impedance spectroscopy (EIS). The EIS evaluation of Leptospirillum sp. interaction with pyrite and surface modified pyrite weathered electrodes revealed significant changes at low frequencies, depending of the compounds presented over the four samples used, including unmodified pyrite and three surface modified samples. Once the frequency at which the adhesion process can become uncover was selected (0.1 and 0.05 Hz), the phase angle variation at such frequency was determined using different microbial concentrations. Different microbial attachment values were obtained for the different electrodes and related to the initial inoculum (2 × 108 cells/mL), as follow: FeS2/Fe(OH)n,S0 (38 ± 3.2%); FeS2/Fe(OH)n (31 ± 5.5%); FeS2 (27 ± 4.7%) and FeS2/S0 (18 ± 3.8%). Microbial attachment to unmodified and modified surfaces, evaluated by EIS, was corroborated with the traditional method of bacterial attachment evaluation by cell count in a Neubauer chamber (r2 = ~0.9). This strategy could be used in developing sensors for the fast and efficient bacterial attachment evaluation in minerals.