Bacterial protein expression systems are easy to culture, grow, and they produce high yields of recombinant protein. They provide fast expression with short doubling time. In addition, they are easy to purify from inclusion bodies. These systems are also easy to scale up by fermentation and can be readily expanded to larger volumes. Other pros are that they are cost-effective for culturing, and easy to manipulate, enabling the introduction of mutations or target genes. Bacterial protein expression systems use fusion tags which help improve protein production yields, folding and solubility, and to facilitate protein purification.