ABSTRACT
Second-generation biofuels produced from non-edible biomasses such as agricultural and animal wastes make the production of fuel more sustainable with zero or negative carbon emissions, and thus are not in direct competition with food production. Biofuel production through metabolic engineering of microorganisms (such as bacteria, yeasts and fungi) has opened a wide range of applications, particularly in the production of environmentally friendly bioethanol, butanol and so on. The reason is that biofuel production through metabolic engineering can increase productivity, increase yield, and also produce second-generation biofuels without depending on fossil fuels. Metabolic engineering has played a crucial role in increasing the production of bioethanol using recombinant strains of Zymomonas mobilis, Escherichia coli and Clostridium thermocellum, and butanol production by Clostridium acetobutylicum, Clostridium cellulolyticum and Klebsiella pneumoniae has been thoroughly detailed in the current chapter. Various molecular biology techniques such as codon optimization, knocking out competitive pathways, RNA interference, CRISPRs or TALENs are common and effective technologies in metabolic engineering. The chapter also presented the future perspective of the technique, showing that other gene-editing techniques such as CRISPR-Cas 9, promoter engineering and artificial transcription factor library can widen the production of environmentally friendly second-generation biofuels.
