Engineering Lignocellulosic Biomass to Single-Cell Oils: Microbial Design, Process Intensification, and Techno-Economic Constraints

Lignocellulosic biomass (LCB) is a readily available nonfood carbon source; nevertheless, its transformation into single-cell oils (SCO) is hindered by its recalcitrant structure, the generation of inhibitors, and energy-intensive downstream processing. This paper outlines the whole LCB-to-SCO value chain, encompassing feedstock composition, pretreatment, enzymatic saccharification, microbial lipogenesis, inhibitor mitigation, bioreactor design, and product recovery. We compile current progress in conventional and contemporary pretreatments, designed enzyme systems, C/N programming, metabolic engineering, and adaptive laboratory evolution that broaden the operational range for oleaginous yeasts and fungi. We focus on how inhibitor profiles, oxygen transfer, and high-solids rheology all work together to determine strain and reactor needs. Throughout the process, techno-economic and life-cycle assessments (TEA/LCA) are used to find unit operations that drive up costs and sustainability problems. We conclude by proposing design concepts and research priorities for biorefineries that accommodate diverse feedstocks, minimize solvent use, and are guided by TEA/LCA. These biorefineries might make LCB-derived SCOs competitive, climate-friendly lipid platforms in the future low-carbon energy and global materials supply chains.