Influence of the white-rot fungus Schizophyllum commune on organically coated sand grains and their heavy metal retention
Fungal alteration of organically coated sand particles, sampled in Eocene sediments in the open cast mining Profen, near Leipzig (Germany) was studied. The organic coatings formed non-continuous layers on quartz grains, measuring few micrometers up to 30 µm in thickness. Such sand particles efficiently retain dissolved metals by adsorption from groundwaters. They consequently can be used as adsorbent to purify low heavy metal contaminated water. However, their stability in the oxic environment and, more specifically, in the presence of microorganisms has not yet been assessed. In order to address this question fungal alteration of organic coatings on sand grains was characterized. Sand grains coated with organic material were incubated on agar medium with and without Schizophyllum commune to estimate topographical and chemical changes. Formation of microbially mediated minerals and etch pits is induced by fungal colonization as shown by SEM. Near-edge X-ray absorption fine structure (NEXAFS) spectra were measured to characterize the different organic compartments with the use of scanning transmission X-ray microscopy (STXM). A relative decrease in aromatic and phenolic groups and a relative enrichment in amide-rich molecules were observed on the altered organic coatings compared to the genuine organic coatings. The results suggest heterogeneous degradation of organic coatings on sand grains influenced by fungal colonization. The sorption capacity of coated sand grains towards Cu was investigated in batch experiments. In the presence of the white-rot fungus, a slight decrease was obtained. Despite this, coated sand grains effectively removed Cu from solution irrespective of the influence from the fungus. In short, the white-rot fungus S. commune alters coated sand grains morphologically and chemically. It can be concluded that long-term exposure to oxidative and fungal degradation may decrease the reliability of coated sand grains in remediation processes.