Screening and Adaptive Evolution of Clostridium for Butanol Synthesis by ABE Fermentation from Cellulosic Biomass: A Review

Abstract

Cellulosic biomass has recently been given considerable attention as the most common renewable
feedstock for biofuel manufacture. However, because of lignocelluloses' complex structure, it must be
processed in several steps, which is expensive and time-consuming. By fermenting cellulosic biomass,
Gram-positive Clostridium species can naturally produce butanol. Therefore, novel microbial
biocatalysts with a higher butanol tolerance are required for the industrial-scale production of butanol.
Due to its natural capability to break down cellulose, the Clostridium bacterium shows excellent
potential as a strain isolated from lignocellulosic feedstocks, agricultural wastes and converted into
butanol. Other species rather than Clostridiun can be used to produce butanol by adaptive evolution.
But, compared to solvent-producing clostridia, other species such as Escherichia
coli and Saccharomyces cerevisiae can adaptively change the butanol pathway that might be a solution for eliminating the formation of major by-products, acetone and ethanol, so that butanol yield
can be improved significantly. Butanol (C4H9OH) is generated primarily using fermentation techniques
and is a powerful industrial solvent. Fermenting cellulosic butanol requires cellulases to break down
lignocellulose into fermentable sugars. Solventogenic Clostridia lack efficient cellulase secretion
abilities, but cellulolytic Clostridia have the innate capability to degrade lignocellulose and generate not
just ethanol and acetate, but also butyrate and potentially even n-butanol. The n-butanol production
process frequently utilized is the ABE fermentation. Also, different target genes employed to
manipulate Clostridium's metabolism in the development of novel microorganisms, and potent synthetic
biology enzymes that exhibit high activity, high production, and butanol robustness are additionally
explored. Sometimes, it is crucial to highlight all challenges encountered and utilize all of the
experiences gained to develop a cost-effective and high-yielding procedure. The objective of this review
is to examine the isolation and evolutionary adaptation of Clostridium species to produce butanol from
cellulosic biomass.