Chemolithotrophic and Autotrophic Growth of Thermothrix thiopara and Some Thiobacilli on Thiosulphate and Polythionates, and a Reassessment of the Growth Yields of Thx. thiopara in Chemostat Culture

SUMMARY: Several thiobacilli and Thermothrix thiopara were grown in chemostat culture with inorganic sulphur compounds as growth-limiting energy substrates for autotrophic growth. Thiobacillus neapolitanus, Thiobacillus thiooxidans and Thiobacillus acidophilus were all able to use thiosulphate, trithionate or tetrathionate as sole energy substrates, as was Thx. thiopara grown at 72 °C. “True growth yields” (Y max) were estimated for the organisms and showed yields of T. neapolitanus to be the same on trithionate and thiosulphate, thereby suggesting that only oxidative, and not substrate-level, phosphorylation is involved in energy conservation in this organism. The yield data suggested that substrate-level phosphorylation could, however, be significant in T. acidophilus. Thiobacillus versutus only grew with thiosulphate, with which it gave yield values similar to those of T. neapolitanus and T. thiooxidans. Thx. thiopara exhibited maximum specific growth rates on thiosulphate, trithionate and tetrathionate of 0·55, 0·23-0·25 and