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

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 surfac es was investigated to further understand the mechanism involved in the lea ching of sulfide minerals. Two strains of Thiobacillus ferrooxidans (DSM 58 3 and ATCC 23270) grown on ferrous iron, sulfur and a chalcopyrite concentr ate were investigated on three sulfide mineral surfaces; pyrite, chalcopyri te and arsenopyrite. The degree of attachment of all substrate grown cells along with contact angle measurements of both minerals and cells were deter mined to evaluate the effect of growth substrate and hydrophobic interactio ns on the attachment process. In addition, concentrations of both ferrous i ron 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 attac hment. 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 alternativ e interaction(s) between the cell and mineral surface is/are principally re sponsible 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 concentration of amyl xanthate decreased t he adhesion of Thiobacillus ferrooxidans. Growth substrate, solution pH, ferrous iron, copper and cobalt ion concentr ations were also investigated with respect to the oxygen consumption of the two strains of Thiobacillus ferrooxidans. Enzyme reaction kinetics were al so 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% su lfur were unable to oxidise similar concentrations of the iron substrate. H owever, following a single subculture onto ferrous iron, sulfur grown cells were able to utilise the ferrous iron substrate all be it at a decreased r ate. Investigation of solution pH suggested both cultures had different opt imum pH values for ferrous iron oxidation. Increasing concentrations of cop per and cobalt (1-100mM) proved to decrease the rate of iron oxidation. (C) 1999 Elsevier Science Ltd. All rights reserved.