Employing synthetic biology to modulate metabolic flux: Current strategies and applications

The world's increasing demand for petrochemical, pharmaceutical, and nutraceutical products necessitates the development of new strategies for producing these high-value chemicals. The depletion of the natural fossil reserves and environmental pollution associated with their procurement further compel us to find sustainable, greener, and cost-effective alternatives. In light of this, a shift has been witnessed in deriving these products from fossil-based sources or chemical synthesis to biomanufacturing (production using living systems). However, to fully utilize the potential of biomanufacturing, novel tools and strategies that can function in bacteria, archaea, and eukaryotes, regulate multi-enzyme pathways, offer precise and conditional gene regulation, and possess versatility are highly required. This review presents a comprehensive summary of the latest gene modulation tools and strategies used by metabolic engineers, along with a mechanistic overview and their applications. In addition, we presented the tools that have the potential to be used for pathway optimization but are still less explored. Within this context, we categorized these tools based on their molecular level of gene regulation, i.e., at and beyond the central dogma. We believe that a deeper understanding of the design, development, and application of these tools would be beneficial for metabolic engineers to reprogram biosynthetic pathways by adopting system-specific approaches, as a single strategy cannot be applied to all systems. Lastly, we discussed the challenges and future prospects of developing these gene regulatory tools to further advance the biomanufacturing field.