Clostridial ABE fermentation

C. acetobutylicum is the model microorganism to study clostridial ABE fermentation. The respective biphasic metabolism is similar to other solventogenic clostridial species (Table 9.1, see Section 9.5). The fermentation starts with uptake of the substrate (e.g., hexoses and pentoses). Sugars are metabolized to... 

Butanol as a Fuel and Chemical Feedstock History of ABE Fermentation Physiology of Clostridial ABE Fermentation... 

As described above, the clostridial ABE fermentative path leads to synthesis of butanol, together with smaller amounts of acetone, ethanol and acetic and butyric acids, together with carhon dioxide and hydrogen (Branduardi et al. 2014). Normally, the solvent ratio of acetone, butanol and ethanol, respectively, is 3 6 1, and the total solvent concentration is around 20 g/L (Connor and Liao 2009). Many natural clostridial strains have the upper butanol tolerance limit at about 11-12 g/L. However, some mutants and engineered strains can tolerate up to 19 g/L of butanol (Jang et al. 2012a). 

Regulation of Solvent Formation in C. acetobutylicum 345 Genetic Tools for Clostridial Species 346 Industrial Application of ABE Fermentation 353 Acknowledgments 355 References 355... 

One of the earliest unconfirmed examples of an ABE fermentation phage infection concerned an abnormal fermentation at the CSC plant in Terre Haute, USA, using maize mash as substrate for a C. acetobutylicum strain [32]. In this instance, the sluggish fermentation lasted for about 1 year and halved the solvent yield. CSC expended considerable efforts into the investigation of the cause of this abnormal fermentation performance and developed a number of countermeasures for preventing its recurrence. These included the use of phage-immunized clostridial... 

So far, the only known natural butanol produced are numerous clostridial species in a process called ABE (acetone-butanol-ethanol) fermentation. Butanol pathway in ABE fermentation consists of condensing two acetyl-CoA molecules (catalysed by a thiolase) and then reducing the product to butanol (requiring four reductases and one dehydratase). Except butanol, acetone and ethanol, Clostridia can also synthesise different chiral substances whose classical chemical synthesis would be challenging (Rogers et al. 1986), and they can degrade several toxic compounds (Francis et al. 1994 Spain 1995). 

Strain degeneration is a known problem of ABE fermentation, especially with continuous operation. Unlike ethanol fermentation by yeast, clostridial fermentation demands constant inoculation with viable cells for the forces to proceed without interruption (Xue et al. 2013a). 

Microorganisms play a vital role in the production of various biorefinery products. For product formation, a particular microbe has to be maintained under specific process conditions. Butanol production by the clostridial acetone-butanol-ethanol (ABE) fermentation... 

The natural producers of butanol are members of the Clostridium family. Clostridium is a rod-shaped, endospore-forming, gram-positive bacterium, strictly anaerobic and xmiver-sally present in the enviroranent (eg, soil and organic waste). Among the clostridial species, Clostridium acetobutylicum and Clostridium beijerinckii are considered to be the best butanol producers. Butanol is naturally synthesized by the Clostridium species in a process called ABE fermentation (Kamm, 2015). 

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