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.