ABSTRACT
Alternative energy-related research currently receives tremendous attention, largely in response to the rising cost of gasoline, and increased depletion of fossil fuel reserves. Consequently, interest in acetone-butanolacetone (ABE) fermentation, which dwindled following the advent of the petrochemical industry, has been revived (Qureshi and Blaschek 2000; Qureshi and Maddox 2005; Yu et al. 2007). However, a major challenge hampering re-commercialization of the ABE process is lack of economic competitiveness, stemming in part from the absence of inexpensive, readily available, and easily fermentable substrates capable of generating high
ABE yields (Qureshi and Blaschek 2000; Yu et al. 2007). Interestingly, solventogenic Clostridium species are capable of fermenting a wide range of carbohydrates (Ezeji and Blaschek 2008), and lignocellulosic biomass has been identified as a potential substrate for inexpensive production of ABE and other fine chemicals (Ezeji and Blaschek 2008; Zhang and Ezeji 2013). However, bioconversion of lignocellulosic biomass is currently plagued by a number of limitations, notably generation of microbial inhibitory compounds during pretreatment and hydrolysis of lignocellulose to mixed sugars (Almeida et al. 2007), and inefficient utilization of the generated mixed sugars by fermenting microorganisms due to carbon catabolite repression (Ren et al. 2010). Therefore, given the broad substrate spectrum of solventogenic Clostridium species (Ezeji and Blaschek 2008; Servinsky et al. 2010; Yu et al. 2007), other cheap and readily utilizable substrates, whose applications in fermentation do not require pretreatment, may prove to be more cost-effective and efficient substrates than lignocellulose.
