Temperature characteristics of bacterial iron solubilisation and 14C assimilation in naturally exposed sulfide ore material at Citronen Fjord, North Greenland (83°N)

Abstract

The presence of iron-solubilising bacteria in the weathered, naturally exposed part of a large sulfide ore deposit (gossan) in the High Arctic (eastern North Greenland, 83°N) was demonstrated. Microscopic examination of ore material and enrichment cultures in minimal medium containing FeS2 or Fe2+ as sole inorganic electron donors revealed the presence of rod-shaped Thiobacillus-like bacteria. When glucose was added as a supplementary energy source to the same enrichment medium, growth of spherical or filamentous acidophilic heterotrophs was observed. Growth kinetics and iron solubilisation activity of acidophilic autotrophs and heterotrophs, respectively, in samples of gossan material were investigated in the temperature range between 0 and 32.5°C. Assimilation of 14C-labelled bicarbonate and glucose occurred at low temperatures (down to 0°C) in both types of enrichments but was optimal around 21°C. It is noteworthy that the rate of dissolved iron (DI=Fe2++Fe3+) production from ore material at 0°C constituted as much as 30% of the maximal value at 21°C. The bacteria involved thus exhibited iron-dissolving activity at the lowest temperature ever reported. An activation energy for DI production of 56 kJ mol−1 K−1 was calculated in the temperature interval from 0 to 17°C. The corresponding H14CO−3 incorporation into biomass at 0°C only amounted to about 5% of the incorporation measured at 21°C. Rates of production were reduced by approximately 25% in incubations amended with glucose as compared to incubations solely containing inorganic compounds. These results indicate that autotrophic bacteria were involved in the solubilisation of iron from the gossan samples.