Technical Communication Growth and hydrogen production characteristics of Caldicellulosiruptor saccharolyticus on chemically defined minimal media Karin Willquist*, Ed W.J. van Niel Applied Microbiology, Lund University, BOX 124, 221 00 Lund, Sweden article info Article history: Received 27 September 2011 Received in revised form 5 November 2011 Accepted 9 December 2011 Available online 2 January 2012 Keywords: Caldicellulosiruptor saccharolyticus Minimal media Hydrogen production Growth activation CO 2 sparging abstract Caldicellulosiruptor saccharolyticus is an extreme thermophilic bacterium recognized for its saccharolytic ability and superior ability to produce high yields of hydrogen. However, most studies have been made using yeast extract (YE) as a rich but expensive nutrient source. For the first time, we show that C. saccharolyticus is able to grow on defined minimal media, including essential vitamins, provided that CO 2 was allowed to accumulate suffi- ciently in the culture broth to activate growth. Growth and hydrogen production perfor- mance on minimal media was analyzed in both batch and continuous mode. Absence of YE resulted in similar or higher hydrogen yields and specific hydrogen productivities but lower volumetric hydrogen productivities than with YE. The results also indicate that YE is used as a carbon- and energy source thus affecting metabolic flux calculations. This study clarified that YE is not essential making C. saccharolyticus more attractive for fundamental studies on its metabolism and future industrial exploitation. Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. 1. Introduction Biological hydrogen production from cellulosic feedstock is considered one of the promising avenues for future bioenergy production. Major economical issues for such a process, however, are the low substrate conversion efficiency [1,2] and high chemical cost [2]. The extreme thermophilic bacterium Caldicellulosiruptor saccharolyticus can produce hydrogen at yields close to the theoretical maximum of the dark fermentation process (i.e., 4 mol H 2 /mol hexose) [3]. The organism is able to ferment an array of mono-, di- and polysaccharides [4e8]and is relatively tolerant to high partial hydrogen pressures, making it a promising candidate for exploitation in a biohydrogen process [9]. It has also been subjected to several fundamental studies due to (i) its extraordinary energy metabolism where pyrophosphate plays a central role [10], (ii) its carbon source-dependent redox metabolism [11]and (iii) its strong link between its redox- and energy metabolism [9,12]. So far metabolic and growth anal- ysis has been performed on media supplemented with yeast extract (YE). The use of YE increases the overall cost of the process significantly [2]. In addition, herein we demonstrate that YE can be used as a carbon- and energy source. There- fore, to adequately estimate metabolic fluxes it is essential to * Corresponding author. Present address: Department of Chemical Engineering, Lund University BOX 124, 221 00 Lund, Sweden. Tel.: þ46 46 2228271; fax: þ46 46 2224526. E-mail addresses: Karin.willquist@tmb.lth.se (K. Willquist), Ed.van_Niel@tmb.lth.se (E.W.J. van Niel). Available online at www.sciencedirect.com journal homepage: www.elsevier.com/locate/he international journal of hydrogen energy 37 (2012) 4925 e4929 0360-3199/$ e see front matter Copyright ª 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijhydene.2011.12.055