The cell attachment and oxygen consumption of two strains of Thiobacillus ferrooxidans

Abstract

Thiobacillus ferrooxidans is a chemolithoautotropic aerobic bacteria which derives energy for its metabolic functions through the oxidation of ferrous iron, sulfur and insoluble sulfides minerals. The attachment of Thiobacillus ferrooxidans cells to sulfide mineral surfaces was investigated to further understand the mechanism involved in the leaching of sulfide minerals. Two strains of Thiobacillus ferrooxidans (DSM 583 and ATCC 23270) grown on ferrous iron, sulfur and a chalcopyrite concentrate were investigated on three sulfide mineral surfaces; pyrite, chalcopyrite and arsenopyrite. The degree of attachment of all substrate grown cells along with contact angle measurements of both minerals and cells were determined to evaluate the effect of growth substrate and hydrophobic interactions on the attachment process. In addition, concentrations of both ferrous iron and the flotation collector potassium amyl xanthate were also studied. Whilst sulfur grown cells exhibited a higher degree of hydrophobicity, both ferrous iron and chalcopyrite grown cells showed a greater degree of attachment. This suggests hydrophobic interactions at the mineral/cell interface are not principally responsible for the attachment process. Differences in the adhesion of the two strains were also observed and suggests alternative interaction(s) between the cell and mineral surface is/are principally responsible for attachment. Increasing the concentration of ferrous iron as a growth substrate resulted in an increase in the degree of cell attachment. Correspondingly, increasing the concenrration of amyl xanthate decreased the adhesion of Thiobacillus ferrooxidans. Growth substrate, solution pH, ferrous iron, copper and cobalt ion concentrations were also investigated with respect to the oxygen consumption of the two strains of Thiobacillus ferrooxidans. Enzyme reaction kinetics were also studied allowing for determination of Km values for ferrous iron similar to those previously reported. Whilst cells grown on ferrous iron were able to oxidise the iron substrate over the range 1–200mM, cells grown on 1% sulfur were unable to oxidise similar concentrations of the iron substrate. However, following a single subculture onto ferrous iron, sulfur grown cells were able to utilise the ferrous iron substrate all be it at a decreased rate. Investigation of solution pH suggested both cultures had different optimum pH values for ferrous iron oxidation. Increasing concentrations of copper and cobalt (1–100mM) proved to decrease the rate of iron oxidation.