A FACULTATIVE THERMOPHILIC THIOBACILLUS-LIKE BACTERIUM: OXIDATION OF IRON AND PYRITE

Abstract

A rod-shaped microbe, isolated from an Icelandic thermal spring grows well at 50° C and oxidises metal sulphides e.g., pyrite (FeS,), pentlandite ((NiFe) SQ) and chalcopyrite (CuFeS,). Initial isolation on a modified ferrous iron medium at pH 3.6 and 60° C indicated that the bacteria were capable of oxidising ferrous iron but that growth was poor. For good growth on sulphide minerals, yeast extract is a requirement. This paper reports on the oxidation of soluble ferrous iron and pyrite by this microbe. The microbe grows slowly at 30° C using ferrous iron but does not grow on pyrite; growth on the latter substrate begins at 40° C. Growth on iron occurs at 50° C, but not at 55° C; growth on pyrite is present at 55° C but not at 60° C. The microbe grows using sulphur as an energy source. The thermophile also grows when yeast extract provides the only apparent energy source. Pyrite-grown cells were used for manometric experiments. Using ferrous iron, the oxygen uptake was non-linear, decreasing with time; the rate increased with increasing pH from 1.3 to 3.2 and also increasing ferrous iron concentration to 8] mM Fe(II). The rate then remained the same at 111mM Fe(II). Using pyrite, the oxygen uptake was linear, the rate being a maximum at pH 2.6. Oxidation of pyrite was slight at pH 1.1 and 3.5. The greatest rate of pyrite oxidation occurred with 100 g c pyrite, the largest concentration tested. Oxygen uptake during the manometric tests with ferrous iron was not greatly affected by the absence of yeast extract; pyrite oxidation was slightly greater without yeast extract. The relevance of the activity of this microbe to biohydrometallurgy is discussed.