The use of microbial expression systems, particularly bacterial expression systems, has revolutionized the field of biotechnology by providing a cost-effective and scalable method for producing proteins. Whether for therapeutic applications in the biopharmaceutical industry or for research purposes, these systems have proven to be versatile and efficient. Biopharmaceutical CDMOs, which often utilize these expression systems, play a critical role in the large-scale production of biologics, ensuring that new therapies reach patients quickly and safely. Additionally, alternative systems such as Pichia pastoris offer advantages for specific types of proteins, broadening the range of applications for microbial expression technologies. The production of proteins like streptolysin highlights the diversity of uses for these systems, demonstrating their value in both clinical and research settings.