Hydrogen production by the hyperthermophilic bacterium Thermotoga maritima part I: effects of sulfured nutriments, with thiosulfate as model, on hydrogen production and growth

Abstract

Background Thermotoga maritima and T. neapolitana are 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, on T. maritima growth, 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.ResultsAmong sulfured nutriments tested, thiosulfate, cysteine, and sulfide were found to be the most efficient to stimulate T. maritima growth and hydrogen production. In particular, under our experimental conditions (glucose 60 mmol L−1 and 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 of T. maritima growth 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 the T. maritima culture medium significantly increased the cellular and hydrogen productivities by a factor 6 without detectable sulfide production.ConclusionsThe stimulant effects of thiosulfate at very low concentrations on T. maritima growth have forced us to reconsider its role in this species and more probably also in all thiosulfato-reducer hyperthermophiles. Henceforth, thiosulfate should be considered in T. maritima as (1) an essential sulfur source for cellular materials when it is present at low concentrations (about 0.3 mmol g−1 of cells), and (2) as both sulfur source and detoxifying agent for H2 when thiosulfate is present at higher concentrations and, when, simultaneously, the pH2 is high. Finally, to improve the hydrogen production in bio-processes using Thermotoga species, it should be recommended to incorporate thiosulfate in the culture medium.

Uncoupling Fermentative Synthesis of Molecular Hydrogen from Biomass Formation in Thermotoga maritima

“…If this toxicity was sufficient to inhibit growth, it could be used to select for mutants that overcame this effect. Since an increase in H 2 partial pressure shifts the metabolism of T. maritima toward lactate synthesis (6,36,37) and not ethanol, transient inactivation of lactate dehydrogenase (encoded by ldh) could exacerbate H 2 toxicity by blocking lactate formation. This would remove one pathway for excretion of excess reductant and thereby create selective pressure to recover such mutants without having to add exogenous H 2 .…”

Biohydrogen production from hyperthermophilic anaerobic digestion of fruit and vegetable wastes in seawater: Simplification of the culture medium of Thermotoga maritima

“…In our study, the growth rate of T. maritima could not be evaluated. However, recent studies showed that it depends on glucose, yeast extract, thiosulfate and dissolved hydrogen concentrations (Boileau et al, 2016;Auria et al, 2016).…”

“…In recent years, pure cultures of Thermotoga maritima have attracted considerable interest for their potential to produce hydrogen from many simple and complex carbohydrates (Huber et al, 1986;Chhabra, 2003;Nguyen et al, 2008;Boileau et al, 2016). This bacterium contains a wide range of thermostable hydrolytic enzymes (cellulases, invertase and xylanases), which are important for hydrolyzing the carbohydrate polymers into monomer sugars (Cappelletti et al, 2012).…”

Specific enrichment of hyperthermophilic electroactive Archaea from deep-sea hydrothermal vent on electrically conductive support

“…The bioelectrochemical system was connected to a semi-automated platform previously described (Boileau et al 2016) to control the composition and rate of gas input (H 2 , CO 2 , O 2 , N 2 ) with mass flowmeters (Bronkhorst, Netherlands). A continuous monitoring of output gas composition (H 2 , N 2 , CH 4 , O 2, CO 2 ) were performed using a micro-GC equipped with a catharometric detector (MS5A, SRA Instrument, France) and a CARBOCAP CO 2 probe (Vaisala GMT 221, Finland).…”