Bacterial and Chemical Interactions with Iron Oxide/Hydroxide Stalagmites Using ATR-IR Spectroscopy and its 4th Derivative Spectra

Abstract Here we report on the chemical interaction between bacteria and fast-growing iron oxide/hydroxide sulphate stalagmites in the abandoned Sitarjevec mine in Slovenia with a low pH (2.2 to 3.4) environment. SEM micrographs revealed distinct morphologies of dry particles from both water and stalagmite layers, as well as the presence of bacterial cells, EPS residue, and biofilm. Bacterial adhesion was studied on the stalagmite surface and inside the stalagmite. Comparison of ATR-IR spectra and the corresponding 2nd and 4th derivative spectra revealed the presence of the P-OFe, COO⁻ and $$\:{\text{S}\text{O}}_{4}^{2-}$$ modes, which are thought to be responsible for bacterial adhesion to the surface and were detected also in the inner part of the stalagmite. To our knowledge, this is the first study of its kind to confirm persistent chemical interactions between iron oxide/hydroxide sulphate-based stalagmite minerals and bacteria on their surface, which is also maintained in the core of the stalagmite.