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.
Highlights
Anthropogenic CO2 emissions have generally been recognized as the major contributor to global warming and associated climate changes
First-generation biofuels are produced from sucrose and starch-rich substrates, which may compete with human consumption - inevitably driving up market prices
One of the reasons to which the low H2 yields observed in mesophilic cultures have been attributed is the thermodynamically unfavourable NADH-dependent H2evolving reaction at PH2 > 0.039 kPa and at standard conditions (1 M concentration of the reactants, 25°C, pH 7) [41]
Summary
Anthropogenic CO2 emissions have generally been recognized as the major contributor to global warming and associated climate changes. C. saccharolyticus can grow and produce H2 from complex lignocellulosic materials, both pre-treated, such as Miscanthus hydrolysate [2], sugar beet juice [34] and paper sludge [23], and untreated, such as wheat straw [35], pine wood [22] and bagasse [35] The fermentation of these raw materials by C. saccharolyticus has yielded H2, CO2 and acetate as the main metabolic end products [2,23,34,35], with a maximum H2 yield per consumed hexose of 3.0-3.8 mol/mol [2,34,35]. Reasons why mesophilic bacteria can produce only 2 moles H2/mol hexose, despite being equipped with the relevant metabolic pathways, are revealed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
