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.