A comparative study of substrate utilisation by Sulfobacillus species in mixed ferrous ion and tetrathionate growth medium

Concurrent ferrous ion and tetrathionate utilisation by Sulfobacillus acidophilus, Sb. thermosulfidooxidans, Sb. thermotolerans, and Sb. sibiricus grown separately in batch culture in dual-substrate media containing ferrous ion and tetrathionate was investigated. For all species, tetrathionate-adapted cells oxidised both substrates concurrently, achieving at least 20% oxidation of the second substrate before the first substrate was exhausted. Sequential substrate utilisation was observed for iron(II)-adapted cells for three of the four species and all iron(II)-adapted cell lines commenced oxidation of ferrous ions ahead of tetrathionate. Adaptation to iron(II) or tetrathionate of the test species had little impact on subsequent ferrous ion oxidation. However, tetrathionate oxidation was affected by growth history. Compared with their respective tetrathionate-adapted cell lines, cells adapted to iron(II) exhibited either significantly longer lag times and/or longer periods to complete tetrathionate oxidation once it had commenced. Polythionate intermediates measured during tetrathionate oxidation to sulfate included thiosulfate, pentathionate and hexathionate for the four species. The intermediate trithionate was only detected in Sb. thermotolerans cultures

Batch culture of Acidithiobacillus caldus on tetrathionate

Acidithiobacillus caldus (DSM 8584) grew aerobically in minimal medium at 45°C with potassium tetrathionate as the sole energy source. Oxidation of tetrathionate during batch culture involved the production of sulfite, thiosulfate, penta- and hexathionate which were then consumed after the tetrathionate was exhausted. Average growth yields over the batch were 3.5g(drywt.)mol(S4O6)-1, somewhat less than yields reported for continuous growth on the same substrate. Thiosulfate was unstable under sterile culture conditions and reacted spontaneously to give tetra-, penta- and hexathionate. It is suggested that the occurrence of polythionates during growth of A. caldus on tetrathionate is due to formation of thiosulfate as the first step in tetrathionate oxidation. Observed growth yields were compared with a thermodynamic framework which suggested a growth efficiency of ca. 10%. The pattern of growth yield and thermodynamic analysis suggest the formation of elemental sulfur although this was not observed

The effects of nitrate on substrate utilisation by some iron(II)- and sulfur-oxidising Bacteria and Archaea

The influence of nitrate on batch cultures of selected Acidithiobacillus, Sulfobacillus, Acidianus, Sulfolobus and Metallosphaera species capable of utilising iron(II) and reduced sulfur substrates was examined. Nitrate was added to cultures in media containing both ferrous ions and tetrathionate. The presence of nitrate resulted in decreased planktonic cell numbers, increased microbial lag times and lower ferrous ion and tetrathionate utilisation rates. These results varied with nitrate concentration, species and adaptive history. Based on the results of batch culture tests, nitrate was added to chalcopyrite concentrate bioleaching experiments to control the redox potential. Bacteria in bioleaching tests at 30 and 45 °C exhibited adaptation to nitrate resulting in high redox potentials. However, when archaea were used in bioleaching tests at 60 °C, ferrous ion oxidation was suppressed in the presence of nitrate. At a nitrate concentration of 20-30 mM, a redox potential of 430-460 mV (vs Ag/AgCl) was maintained during the 10 week experiment. At this redox potential copper extraction was increased by 20% compared to a culture without nitrate, potentially offering a method of redox control for high-temperature stirred-tank bioleaching with archaea

Substrate utilisation by Sulfobacillus thermosulfidooxidans in mixed ferrous ion and tetrathionate growth medium

Sulfobacillus thermosulfidooxidans cultures adapted to ferrous or tetrathionate ions were inoculated into media containing both substrates. In batch culture, cells showed a preference for oxidising ferrous ion followed by tetrathionate. Tetrathionate oxidation was slower in ferrousadapted cells. Biomass formation exhibited an exponential growth phase during ferrous ion oxidation followed by an exponential growth phase during tetrathionate oxidation. Sequential utilisation of ferrous ion followed by tetrathionate ion was observed when equimolar amounts of substrates or electron-equivalent amounts were provided

Substrate utilisation and chalcopyrite concentrate bioleaching at 60°c in the presence of nitrate

In batch cultures, the presence of nitrate inhibited iron(II) oxidation by iron(II)- or tetrathionate-adapted Acidianus (A.) brierleyi and Sulfolobus (S.) metallicus cells and tetrathionate oxidation by iron(II)-adapted A. brierleyi cells. Tetrathionate-adapted cell lines of A. brierleyi and S. metallicus oxidised tetrathionate in the presence of up to 40 mM nitrate but cell numbers were lower than those in uncontaminated tests. The results of the bioleaching tests indicated a possible window of enhanced copper extraction in the presence of 20-30 mM nitrate that might be exploited in tank bioleaching. The build up of nitrate above 40 mM in bioleaching solutions must be avoided

The resilience and versatility of acidophiles that contribute to the bio-assisted extraction of metals from mineral sulphides

In this paper, a brief outline is presented on acidic ferric ion oxidation of mineral sulphides for the extraction of metals in both stirred tank reactors for mineral concentrates and heaps for low-grade ores. The identities and capabilities of the relatively few acidophiles that assist the oxidative processes are summarized and their responses to selected extremes in their growth environments described. Individually, the organisms adapt to the presence of high concentrations of heavy metals and other elements in the bioleaching environment, tolerate a wide range of acidities and can recover from prolonged exposure to temperatures significantly above their preferred temperatures for growth. However, the presence of chloride in their acidic environment presents a significant physiological challenge. Species that exhibit a chemotactic response and attachment to sulphide surfaces, where they can create their own micro-environments, would be favoured in both heap bioreactors with low availability of energy substrates and physically aggressive, agitated continuous stirred-tank reactor environments treating concentrates

Population dynamics of a low-grade chalcopyrite bioleaching column

Terminal Restriction Fragment Length Polymorphism (T-RFLP) was used to determine the diversity of the bacterial and archaeal populations in a bioleaching column charged with a lowgrade chalcopyrite ore and operated at 50 oC. Differing populations were identified in the leachate and the column solids but there was not discernible effect in respect of location in the column

The effect of ferrous iron addition during tetrathionate utilisation by some sulfobacillus species

Ferrous sulfate was added to batch cultures of Sulfobacillus (Sb.) acidophilus, Sb. thermosulfidooxidans and Sb. sibiricus at the start of the exponential growth phase during growth on tetrathionate. Soluble ferrous ion and polythionate concentrations were used as a measure of substrate utilisation. Sb. thermosulfidooxidans switched from utilising polythionates to exclusively oxidising ferrous ions, only then oxidising the remainder of the polythionates. Sb. sibiricus and Sb. acidophilus did not cease polythionate oxidation but utilised both substrates concurrently after ferrous ion addition. None of the cultures tested exhibited preferential polythionate utilisation, even though they were utilising polythionate prior to the addition of ferrous ions