title: Hydrogen production by the hyperthermophilic bacteriumThermotoga maritimapart I: effects of sulfured nutriments, with thiosulfate as model, on hydrogen production and growth.
abstract: BACKGROUND
  Thermotoga maritimaandT. neapolitanaare hyperthermophile bacteria chosen by many research teams to produce bio-hydrogen because of their potential to ferment a wide variety of sugars with the highest theoretical H2/glucose yields. However, to develop economically sustainable bio-processes, the culture medium formulation remained to be optimized. The main aim of this study was to quantify accurately and specifically the effect of thiosulfate, used as sulfured nutriment model, onT. maritimagrowth, yields and productivities of hydrogen. The results were obtained from batch cultures, performed into a bioreactor, carefully controlled, and specifically designed to prevent the back-inhibition by hydrogen.
  
  
  RESULTS
  Among sulfured nutriments tested, thiosulfate, cysteine, and sulfide were found to be the most efficient to stimulateT. maritimagrowth and hydrogen production. In particular, under our experimental conditions (glucose 60 mmol L-1and yeast extract 1 g L-1), the cellular growth was limited by thiosulfate concentrations lower than 0.06 mmol L-1. Under these conditions, the cellular yield on thiosulfate (Y X/Thio) could be determined at 3617 mg mmol-1. In addition, it has been shown that the limitations ofT. maritimagrowth by thiosulfate lead to metabolic stress marked by a significant metabolic shift of glucose towards the production of extracellular polysaccharides (EPS). Finally, it has been estimated that the presence of thiosulfate in theT. maritimaculture medium significantly increased the cellular and hydrogen productivities by a factor 6 without detectable sulfide production.
  
  
  CONCLUSIONS
  The stimulant effects of thiosulfate at very low concentrations onT. maritimagrowth have forced us to reconsider its role in this species and more probably also in all thiosulfato-reducer hyperthermophiles. Henceforth, thiosulfate should be considered inT. maritimaas (1) an essential sulfur source for cellular materials when it is present at low concentrations (about 0.3 mmol g-1of cells), and (2) as both sulfur source and detoxifying agent for H2when thiosulfate is present at higher concentrations and, when, simultaneously, the pH2is high. Finally, to improve the hydrogen production in bio-processes usingThermotogaspecies, it should be recommended to incorporate thiosulfate in the culture medium.
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Céline
authors.initials: C
authors.lastname: Boileau
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Richard
authors.initials: R
authors.lastname: Auria
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Sylvain
authors.initials: S
authors.lastname: Davidson
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Laurence
authors.initials: L
authors.lastname: Casalot
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Pierre
authors.initials: P
authors.lastname: Christen
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Pierre-Pol
authors.initials: PP
authors.lastname: Liebgott
authors.affiliation: Aix Marseille Université, CNRS, Université de Toulon, IRD, MIO UM 110, 13288 Marseille, France.
authors.forename: Yannick
authors.identifier: 0000-0003-2694-1100
authors.initials: Y
authors.lastname: Combet-Blanc
keywords: Glucose; Growth; Hydrogen; Metabolism; Productivity; Sulfured nutriments; Thermotoga maritima; Thiosulfate; Yields