Weathering-associated bacteria from the Damma glacier forefield: physiological capabilities and impact on granite dissolution

Abstract

Several bacterial strains isolated from granitic rock material in front of the Damma glacier (Central Swiss Alps) were shown (i) to grow in the presence of granite powder and a glucose-NH(4)Cl minimal medium without additional macro- or micronutrients and (ii) to produce weathering-associated agents. 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.

FIG. 1.

Total cell counts (mean ± standard error; n = 3) of sessile (filled bars) and planktonic (empty bars) cells after 16 days of dissolution experiments. Batch reactors contained 3 g of granite and 90 ml of growth medium. The dashed line shows the initial cell numbers (at time zero). The investigated isolates are represented as follows: A, Arthrobacter sp.; B, Frigoribacter sp.; C, Paenibacillus sp.; D, Janthinobacterium sp.; E, Leifsonia sp.; F, Oxalobacter sp.; G, Paucibacter sp.; H, Pedobacter steynii; I, Polaromonas sp.; J, Pseudomonas sp.; K, Rhodococcus erythropolis; L, Variovorax sp.; and GA, Chlorella sp.

FIG. 2.

Changes of pH (mean; n = 3) in solution over time (0, 1, 2, 4, 8, and 16 days). Results are shown for biotic experiments with granite containing bacteria (A to L) or green algae (GA) and for abiotic controls with granite containing 3.3 mM glucose (Me⁺). The investigated isolates are represented as follows: A, Arthrobacter sp; B, Frigoribacter sp.; C, Paenibacillus sp.; D, Janthinobacterium sp.; E, Leifsonia sp.; F, Oxalobacter sp.; G, Paucibacter sp.; H, Pedobacter steynii; I, Polaromonas sp.; J, Pseudomonas sp.; K, Rhodococcus erythropolis; L, Variovorax sp.; and GA, Chlorella sp.

FIG. 3.

Iron concentration (μM; mean ± standard error; n = 3) in solution over time, quantified with the ferrozine method. (a) Biotic experiments with granite containing bacteria (A to L) or green algae (GA) and growth medium (glucose-ammonium chloride) alone. (b) Abiotic controls with granite containing 3.3 mM glucose (Me⁺), 10 mM oxalic acid (Ox), 3 mM citric acid (Cit), 1 mM HCl (HCl), or 1 mm KCN (CN⁻). The investigated isolates are represented as follows: A, Arthrobacter sp.; B, Frigoribacter sp.; C, Paenibacillus sp.; D, Janthinobacterium sp.; E, Leifsonia sp.; F, Oxalobacter sp.; G, Paucibacter sp.; H, Pedobacter steynii; I, Polaromonas sp.; J, Pseudomonas sp.; K, Rhodococcus erythropolis; L, Variovorax sp.; and GA, Chlorella sp.

FIG. 4.

Formation of metabolites during the dissolution experiments with granite. (a) Concentrations of oxalic acid (μM; mean ± standard error; n = 3) in solution after 8 and 16 days of incubation. (b) Concentrations of CN⁻ (μM; mean ± standard error) over time. The investigated isolates are represented as follows: A, Arthrobacter sp.; B, Frigoribacter sp.; C, Paenibacillus sp.; D, Janthinobacterium sp.; E, Leifsonia sp.; F, Oxalobacter sp.; G, Paucibacter sp.; H, Pedobacter steynii; I, Polaromonas sp.; J, Pseudomonas sp.; K, Rhodococcus erythropolis; L, Variovorax sp.; and GA, Chlorella sp. Results are shown for abiotic controls containing 3.3 mM glucose with (Me⁺) or without (Me⁻) granite.

FIG. 5.

Relationships between oxalic acid (μM) and iron concentrations (μM) in solution during the experiment, n = 78 (a), between CN⁻ (μM) and Fe (μM) concentrations (n = 195) (b), and between pH and iron concentration (μM; n = 195) (c).