Acidophilic leaching microorganisms are of industrial interest to extract metals from ores. The effect of characteristics such as rugosity, charge, and composition on the colonization of bioleaching bacteria is not yet fully understood. Since cell colonization on pyrite (FeS2) surfaces is highly heterogeneous, robust massive image analysis methods must be employed.
We investigated the effects of rational modifications of pyrite surfaces on early colonization and biofilm formation ability of bioleaching bacteria. We used confocal laser scanning microscopy (CLSM), atomic force microscopy (AFM), Raman spectroscopy, and field emission scanning electron microscopy (FE-SEM) with energy-dispersive spectroscopy (EDS) to characterize the surface of pyrite coupons polished to varying degrees. We further colonized the polished pyrite with three bioleaching strains: Leptospirillum ferriphilum, Acidiferrobacter SP3, and Acidithiobacillus ferrooxidans R1. After 24 h of colonization, samples were imaged using EFM, and massive sets of 176-384 images per replicate were analyzed and semi-quantified using custom-made Python scripts and open-source libraries to obtain the colonization density, area, and shape of cell colonies. The data suggest a slight increase in colonization area in medium polished samples in comparison to low polished ones, but a decrease on highly polished samples. However, Kruskal-Wallis test with multiple comparisons indicated no significant differences in other cell colonization parameters among the different samples.