10.4.1 Modeling

First attempts to model the ABE fermentation were already undertaken in the 1980s (Voturba et al., 1986) based on mass balances for the substrate, biomass, key intermediates and products of C. acetobutylicum batch cultures. Better models were proposed when various on-line measurements (Chauvatcharin et al., 1998; Junne et al., 2008) and the genome sequences of C. acetobutylicum (Nolling et al., 2001) and later on C. beijerinckii (JGI, 2005) became available. Meanwhile, the study of transcriptome (Alsaker and Papoutsakis, 2005; Alsaker et al, 2004; Jones et al., 2008; Shi and Blashek, 2008; Tomas et al, 2003a, 2003b; Tomas et al., 2004; Tummala, Junne, Paredes, et al., 2003), proteome (Schwarz et al, 2007; Sullivan and Bennet, 2006) and metabolome (Shinto et al., 2007) of different solventogenic clostridia leads to more complex and comprehensive models (Junne et al., 2008; Senger and Papoutsakis, 2008a, 2008b; Shinto et al., 2007), which supported further understanding of the clostridial metabolism and allowed predictions of metabolic fluxes and end-products for several scenarios. However, the biphasic nature of the metabolism and the complex regulatory networks (see Section 10.2) still cause some problems that can result in incorrect outputs. The assumed reversibility of enzymatic activities lacks experimental evidence in several cases. Also, the obvious pH influence on the shift to solventogenesis has been neglected in some models. A transnational research network is currently focusing on elucidating systems biology of solventogenesis in C. acetobutylicum (project COSMIC within the SysMO program, www. sysmo. net).