Physiological characteristics of the extreme thermophile Caldicellulosiruptor saccharolyticus: an efficient hydrogen cell factory

Abstract

Global concerns about climate changes and their association with the use of fossil fuels have accelerated research on biological fuel production. Biological hydrogen production from hemicellulose-containing waste is considered one of the promising avenues. A major economical issue for such a process, however, is the low substrate conversion efficiency. Interestingly, the extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus can produce hydrogen from carbohydrate-rich substrates at yields close to the theoretical maximum of the dark fermentation process (i.e., 4 mol H2/mol hexose). The organism is able to ferment an array of mono-, di- and polysaccharides, and is relatively tolerant to high partial hydrogen pressures, making it a promising candidate for exploitation in a biohydrogen process. The behaviour of this Gram-positive bacterium bears all hallmarks of being adapted to an environment sparse in free sugars, which is further reflected in its low volumetric hydrogen productivity and low osmotolerance. These two properties need to be improved by at least a factor of 10 and 5, respectively, for a cost-effective industrial process. In this review, the physiological characteristics of C. saccharolyticus are analyzed in view of the requirements for an efficient hydrogen cell factory. A special emphasis is put on the tight regulation of hydrogen production in C. saccharolyticus by both redox and energy metabolism. Suggestions for strategies to overcome the current challenges facing the potential use of the organism in hydrogen production are also discussed.

Design of a novel biohythane process with high H2 and CH4 production rates

“…Based on previous knowledge, the main concerns when designing DF using C. saccharolyticus are the sensitivity of this thermophile to elevated levels of H 2aq and osmotic pressure [3,18]. In addition, inhibitors in the wheat straw hydrolysate may affect the fermentation profile.…”

“…In a conventional dark fermentation (DF) process only about 7.5e15% of the energy contained in glucose is converted to H 2 (corresponding to a yield of 1e2 mol H 2 per mole glucose the rest of the energy is contained in volatile fatty acids (VFA)) [2]. Fortunately, recent progress in the characterisation of new potential organisms has revealed a number of organisms providing better H 2 yields [3]. Caldicellulosiruptor saccharolyticus, is one such organism, and is able to produce almost the theoretical maximum yield of 4 mol H 2 per mole glucose [4].…”

“…Caldicellulosiruptor saccharolyticus, is one such organism, and is able to produce almost the theoretical maximum yield of 4 mol H 2 per mole glucose [4]. In addition, C. saccharolyticus can grow on hemicellulosic waste [5e9], and can grow and produce H 2 at partial H 2 pressures (P H2 ) of up to 0.67 bar [3]. However, 65% of the energy contained in the glucose still remains in the liquid as acetate.…”

Extremophiles and their Application to Biofuel Research

“…Variants of Caldicellulosiruptor saccharolyticus (Herbel et al, 2010;Willquist et al, 2010) and Thermotogoelfii (de Vrije et al, 2009;Schut and Adams, 2009;Nguyen et al, 2010) show particular promise as organisms able to mediate the conversion of organic compounds to hydrogen. Hydrogen capacities of the archaeal genera Thermococcus and Pyrococcus (Silva et al, 2000;Kanai et al, 2005), and bacterial strains belonging to the genera Thermoanaerobacter and Thermotogales (Nandi and Sengupta, 1998;Nandi et al, 2001;Bagi et al, 2007;Shaw et al, 2008a) have been reported.…”

Dissecting and engineering metabolic and regulatory networks of thermophilic bacteria for biofuel production

“…1) (Chang and Yao, 2011;Demain et al, 2005;Lin et al, 2011;Taylor et al, 2009). Moreover, TGPAs, such as Caldicellulosiruptor saccharolyticus, are capable of producing hydrogen from lignocellulosic and waste materials (Willquist et al, 2010).…”