Microbial engineering for the production of isobutanol: current status and future directions

Abstract

Fermentation-derived alcohols have gained much attention as an alternate fuel due to its minimal effects on atmosphere. Besides its application as biofuel it is also used as raw material for coating resins, deicing fluid, additives in polishes, etc. Among the liquid alcohol type of fuels, isobutanol has more advantage than ethanol. Isobutanol production is reported in native yeast strains, but the production titer is very low which is about 200 mg/L. In order to improve the production, several genetic and metabolic engineering approaches have been carried out. Genetically engineered organism has been reported to produce maximum of 50 g/L of isobutanol which is far more than the native strain without any modification. In bacteria mostly last two steps in Ehrlich pathway, catalyzed by enzymes ketoisovalerate decarboxylase and alcohol dehydrogenase, are heterologously expressed to improve the production. Native Saccharomyces cerevisiae can produce isobutanol in negligible amount since it possesses the pathway for its production through valine degradation pathway. Further modifications in the existing pathways made the improvement in isobutanol production in many microbial strains. Fermentation using cost-effective lignocellulosic biomass and an efficient downstream process can yield isobutanol in environment friendly and sustainable manner. The present review describes the various genetic and metabolic engineering practices adopted to improve the isobutanol production in microbial strains and its downstream processing.

Economics and global warming potential of a commercial-scale delignifying biorefinery based on co-solvent enhanced lignocellulosic fractionation to produce alcohols, sustainable aviation fuels, and co-products from biomass

“…Solids loading in CBP of CELF-derived cellulose to isobutanol was dialed down accordingly to 8.5% so as to reach a maximum titer of 30 g L À1 for this alcohol in comparison to ethanol (capped at 75 g L À1 ). Although more advanced technologies for the recovery of isobutanol, such as the in situ removal of the alcohol, 63,64 could potentially allow for higher titers in the fermentation broththese methods have not yet been demonstrated to improve CBP of CELF-derived cellulose.…”

New regulatory role of Znf1 in transcriptional control of pentose phosphate pathway and ATP synthesis for enhanced isobutanol and acid tolerance

“…Isobutanol is a branched‐chain alcohol produced naturally in very small amounts by the yeast S. cerevisiae via the valine biosynthetic and Ehrlich pathway (Hussain et al, 2022; Lakshmi et al, 2021). To increase isobutanol production in yeasts, overexpression of valine biosynthesis and Ehrlich pathway genes (namely ILV2 , ILV5 , ILV3 , BAT1 , and BAT2 ) (Liu et al, 2021), elimination of competing pathway genes to block production of ethanol, 2,3 butanediol, pantothenate and isolucine (Ida et al, 2015), and deletion of PDC1 gene encoding key enzyme pyruvate decarboxylase in alcoholic fermentation have been executed (Matsuda et al, 2013).…”

“…To increase isobutanol production in yeasts, overexpression of valine biosynthesis and Ehrlich pathway genes (namely ILV2 , ILV5 , ILV3 , BAT1 , and BAT2 ) (Liu et al, 2021), elimination of competing pathway genes to block production of ethanol, 2,3 butanediol, pantothenate and isolucine (Ida et al, 2015), and deletion of PDC1 gene encoding key enzyme pyruvate decarboxylase in alcoholic fermentation have been executed (Matsuda et al, 2013). However, isobutanol synthesis in the yeast S. cerevisiae has remained lower than the theoretical value and much less in comparison to that of the bacteria counterpart (Lakshmi et al, 2021).…”

Experimental Study of Physical-Chemical Properties of Advanced Alcohol-to-Jet Fuels

“…These technologies are discussed in detail in studies by Silveira et al (2018), Yamada et al (2011). Butanol and isobutanol are also used for the AtJ process and are usually produced by fermentation with modified microorganisms (Fu et al, 2021;Lakshmi et al, 2021). Today companies-producers of AtJ fuel usually specialize in a certain type of alcohol (Achinas et al, 2021;Geleynse et al, 2018).…”