. In particular, four bacterial isolates (one isolate each of Arthrobacter sp., Janthinobacterium sp., Leifsonia sp., and Polaromonas sp.) were weathering associated. In comparison to what was observed in abiotic experiments, the presence of these strains caused a significant increase of granite dissolution (as measured by the release of Fe, Ca, K, Mg, and Mn). These most promising weathering-associated bacterial species exhibited four main features rendering them more efficient in mineral dissolution than the other investigated isolates: (i) a major part of their bacterial cells was attached to the granite surfaces and not suspended in solution, (ii) they secreted the largest amounts of oxalic acid, (iii) they lowered the pH of the solution, and (iv) they formed significant amounts of HCN. As far as we know, this is the first report showing that the combined action of oxalic acid and HCN appears to be associated with enhanced elemental release from granite, in particular of Fe. This suggests that extensive microbial colonization of the granite surfaces could play a crucial role in the initial soil formation in previously glaciated mountain areas.

Fungi were isolated from fine granitic sediments, which were collected at 15 sampling points within a 20 m × 40 m area in front of the Damma glacier in the central Swiss Alps. From the 45 fungal isolates grown on nutrient-rich agar media at 4 °C, 24 isolates were selected for partial sequencing and identification based on the small subunit ribosomal DNA. Sequencing data revealed that the isolated fungi represented three fungal phyla and 15 species. The weathering potential of 10 of the 15 fungal species was tested with dissolution experiments using powdered granite material (<63 μm). The results showed that the zygomyceteous species Mucor hiemalis, Umbelopsis isabellina and Mortierella alpina dissolved the granite powder most efficiently due to the release of a variety of organic acids, mainly citrate, malate and oxalate. In particular, the high concentrations of Ca, Fe, Mg and Mn in the solutions clustered well with the high amounts of exuded citrate. This is the first report on fungi that were isolated from a non-vegetated glacier forefield in which the fungi's capabilities to dissolve granite minerals were examined.