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

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.