TEMPERATURE CHARACTERISTICS OF BACTERIAL IRON SOLUBILIZATION AND C-14ASSIMILATION IN NATURALLY EXPOSED SULFIDE ORE MATERIAL AT CITRONEN FJORD, NORTH GREENLAND (83-DEGREES-N)

The presence of iron-solubilising bacteria in the weathered, naturally exposed part of a large sulfide ore deposit (gossan) in the High Arct ic (eastern North Greenland, 83 degrees N) was demonstrated. Microscop ic examination of ore material and enrichment cultures in minimal medi um containing FeS2 or Fe2+ as sole inorganic electron donors revealed the presence of rod-shaped Thiobacillus-like bacteria. When glucose wa s added as a supplementary energy source to the same enrichment medium , growth of spherical or filamentous acidophilic heterotrophs was obse rved. Growth kinetics and iron solubilisation activity of acidophilic autotrophs and heterotrophs, respectively, in samples of gossan materi al were investigated in the temperature range between 0 and 32.5 degre es C. Assimilation of C-14-labelled bicarbonate and glucose occurred a t low temperatures (down to 0 degrees C) in both types of enrichments but was optimal around 21 degrees C, It is noteworthy that the rate of dissolved iron (DI = Fe2++Fe3+) production from ore material at 0 deg rees C constituted as much as 30% of the maximal value at 21 degrees C , The bacteria involved thus exhibited iron-dissolving activity at the lowest temperature ever reported. An activation energy for DI product ion of 56 kJ mol(-1) K-1 was calculated in the temperature interval fr om 0 to 17 degrees C. The corresponding (HCO3-)-C-14 incorporation int o biomass at 0 degrees C only amounted to about 5% of the incorporatio n measured at 21 degrees C. Rates of production were reduced by approx imately 25% in incubations amended with glucose as compared to incubat ions solely containing inorganic compounds. These results indicate tha t autotrophic bacteria were involved in the solubilisation of iron fro m the gossan samples.