Evaluation of assimilatory sulphur metabolism in Caldicellulosiruptor saccharolyticus

•C. saccharolyticus can assimilate sulphate and grow in absence of a reducing agent.•Majority of Caldicellulosiruptor species possess genes for sulphate assimilation.•C. saccharolyticus   tolerates high PH2PH2 regardless of sulphur source used.•Sulphate can replace cysteine in the cultivation medium of C. saccharolyticus.

Caldicellulosiruptor saccharolyticus has gained reputation as being among the best microorganisms to produce H2 due to possession of various appropriate features. The quest to develop an inexpensive cultivation medium led to determine a possible replacement of the expensive component cysteine, i.e. sulphate. C. saccharolyticus assimilated sulphate successfully in absence of a reducing agent without releasing hydrogen sulphide. A complete set of genes coding for enzymes required for sulphate assimilation were found in the majority of Caldicellulosiruptor species including C. saccharolyticus. C. saccharolyticus displayed indifferent physiological behaviour to source of sulphur when grown under favourable conditions in continuous cultures. Increasing the usual concentration of sulphur in the feed medium increased substrate conversion. Choice of sulphur source did not affect the tolerance of C. saccharolyticus to high partial pressures of H2. Thus, sulphate can be a principle sulphur source in an economically viable and more sustainable biohydrogen process using C. saccharolyticus.