Engineering genetic elements for microbial protein expression systems: Advances, challenges, applications, and prospects.

The rising global demand for sustainable protein sources poses critical challenges across food, pharmaceutical, and industrial biotechnology sectors. Microbial expression systems provide scalable and versatile platforms for producing recombinant proteins, including enzymes, therapeutic molecules, and functional food ingredients. These platforms enable efficient biosynthesis of high-value proteins from renewable substrates often via precision fermentation, surpassing conventional methods in yield, cost-efficiency, and environmental sustainability. This review summarizes the genetic regulatory elements that govern gene expression in microbial hosts, with comparative coverage of prokaryotic and eukaryotic systems at transcriptional and translational levels. Key regulatory components, such as promoters, ribosome binding sites (RBS), untranslated regions (UTRs), signal peptides, and terminators, are discussed in the context of host-specific engineering strategies. We highlight advanced engineering approaches, including artificial intelligence (AI) assisted sequence design, CRISPR-Cas-based genome editing, and modular combinatorial optimization of genetic elements. Particular attention is given to the integration of high-throughput screening and predictive modeling tools that accelerate the rational design and optimization of microbial production systems. The review also discusses practical applications in food, pharmaceutical, and industrial enzyme production, emphasizing how genetic element engineering bridges fundamental research and biomanufacturing. Finally, key challenges and future prospects are analyzed to guide the development of next-generation microbial cell factories for sustainable protein production and industrial innovation.