Batch culture of Acidithiobacillus caldus on tetrathionate

Abstract

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 3.5 g(dry wt.) mol(S 4O 6) −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.