Opportunities and challenges for n-alkane and n-alkene biosynthesis: A sustainable microbial biorefinery

Alkanes and alkenes are high-value platform chemicals that can be synthesized by microorganisms, utilizing organic residues from agri-food industries and municipalities, thereby offering an alternative opportunity in resource recovery. Current research and technological advancements for the biosynthesis of alkanes and alkenes are mainly impeded by low product titers, obstructing the bioprocess upscaling and large-scale applications. Thus, current scientific investigations aim to improve productivity by utilizing natural and engineered metabolic pathways in various microbial chassis to suppress competing metabolic pathways, coupled with bioprocess optimization. Additionally, to reduce costs, research is being conducted on utilizing inorganic carbon sources such as CO₂ to promote the green synthesis of alkanes and alkenes. Therefore, this review critically discusses the opportunities and challenges in alkane and alkene biosynthesis, aiming to examine the current technological advancements. In this review, the limitations of five major metabolic pathways for alkane and alkene biosynthesis are thoroughly discussed, highlighting their shortcomings. Additionally, various techniques, including metabolic engineering, autotrophic metabolic pathways, and new non-biosynthetic routes, are investigated as potential methods to enhance product titers. Furthermore, this review offers valuable insights into the economic and environmental aspects of alkane and alkene biosynthesis while also presenting perspectives for future research directions.