Synthetic biology and metabolic engineering paving the way for sustainable next-gen biofuels: a comprehensive review

Biofuels are pivotal in transitioning to sustainable energy systems, offering renewable alternatives to fossil fuels with reduced emissions. This review examines the evolution of biofuel production, contrasting first-generation biofuels derived from food crops with second-generation biofuels from non-food lignocellulosic feedstock. This review evaluates social and environmental impacts, with a focus on land use, energy efficiency, and scalability. Advances in synthetic biology and metabolic engineering have revolutionized biofuel production by optimizing microorganisms like bacteria, yeast, and algae for enhanced substrate processing and industrial resilience. Key enzymes, such as cellulases, hemicellulases, and ligninases, facilitate the conversion of lignocellulosic biomass into fermentable sugars. CRISPR-Cas systems enable precise genome editing, while de novo pathway engineering produces advanced biofuels such as butanol, isoprenoids, and jet fuel analogs, boasting superior energy density and compatibility with existing infrastructure. Notable achievements include 91% biodiesel conversion efficiency from lipids and a 3-fold butanol yield increase in engineered Clostridium spp., alongside ∼85% xylose-to-ethanol conversion in S. cerevisiae. However, commercial scalability is hindered by biomass recalcitrance, limited yields, and economic challenges. Emerging strategies, including consolidated bioprocessing, adaptive laboratory evolution, and AI-driven strain optimization, address these barriers. This review also explores biofuel integration within circular economy frameworks, emphasizing waste recycling and carbon-neutral operations. Multidisciplinary research is essential to enhance economic viability and environmental sustainability, ensuring biofuels play a central role in global renewable energy systems.