Design of Microbial Cell Factories for Lignocellulosic Biorefinery

The biorefinery manufacturing process for producing chemicals and liquid fuels from biomass is a promising approach for securing energy and resources. Establishing economically feasible fermentation processes requires markedly increasing final product titers due to the high energy demands of subsequent product recovery steps, as well as the capital and production costs associated with biorefinery equipment. Although high-yield production of target compounds by metabolically optimized microbes is necessary, achieving higher titers inevitably requires increased loading of solid lignocellulose in the SSF and CBP processes. Increase in the solid concentration results in corresponding increases in chemical production. However, by increasing the lignocellulose content in the bioreactor, the concentration of fermentation inhibitors released during the pretreatment of biomass would reach higher levels. Accordingly, microorganisms that are resistant to inhibitors are a prerequisite for the high-titer production of fuels and chemical products. To further engineer cellulolytic recombinant and native strains for use in CBP, system-wide modifications of intracellular metabolic pathways using advanced engineering tools such as minimal hosts, vectors, genetic controllers, and characterized enzymes are needed, which would improve the potential of not only target productivities but cell growth and viability during the fermentation. The integration of cellulolytic capabilities with metabolic systems specified for targeted chemical production will allow customized CBP microorganisms to be developed using advanced gene manipulation technologies.