Economical challenges to microbial producers of butanol: Feedstock, butanol ratio and titer

Abstract

Butanol is an important solvent and transport fuel additive, and can be produced by microbial fermentation. Attempts to generate a superior microbial producer of butanol have been made through different metabolic engineering strategies. However, to date, butanol bio-production is still not economically competitive compared to petrochemical-derived production because of its major drawbacks, such as, high cost of the feedstocks, low butanol concentration in the fermentation broth and the co-production of low-value by-products acetone and ethanol. Here we analyze the main bottlenecks in microbial butanol production and summarize relevant advances from recently reported studies. Further needs and directions for developing real industrially applicable strains in butanol production are also discussed.

Phosphoketolase Pathway for Xylose Catabolism in Clostridium acetobutylicum Revealed by 13 C Metabolic Flux Analysis

“…The GC-MS data were analyzed as described previously (26). Briefly, a mass isotopomer distribution vector (MDV) of each fragment of alanine, glycine, valine, serine, phenylalanine, histidine, and tyrosine was determined from the respective mass spectra and was corrected for the natural abundance of all stable isotopes, including 13 C, 29 Si, 30 Si, 15 N, and 18 O. From the MDV of the amino acids, the MDVs of their respective precursor intermediates, including 3-P-glycerate, phosphoenolpyruvate (PEP), pyruvate, ribose-5-P, and erythrose-4-P, could be easily derived.…”

“…To reduce the substrate cost, abundant and inexpensive lignocellulosic materials could be used, and one of their major components is pentose-rich hemicellulose (15). Solventogenic clostridia, including Clostridium acetobutylicum and Clostridium beijerinckii, are capable of utilizing the hemicellulosic pentoses xylose and arabinose (25).…”

Recent advances on biobutanol production

“…The cost of feedstock represents over 70% of the total production costs of biobutanol [63]. At the beginning of butanol fermentation, substrates based on sugars and starch were used, but these are expensive and the process becomes unfeasible.…”

Enhanced production of butanol and acetoin by heterologous expression of an acetolactate decarboxylase in Clostridium acetobutylicum

“…As an important chemical and a 2nd generation biofuel that is a potential substitute for petrol-derived fuels, bio-butanol has attracted the attention of scientists in recent years (Green, 2011;Tracy, 2012). However, current bio-butanol production processes lack economic competitiveness due to high raw material cost, poor atom economy (low conversion rate of sugar to alcohols, lots of byproducts, and severe gas emission), low solvent titer and productivity, and high energy consumption and water usage in product recovery (Gu et al, 2011;Jones and Woods 1986).…”