What are the advantages and disadvantages of bacterial expression system?

The most commonly used expression system is the bacterium E.coli expression system. It has the advantages of fast breeding, low cost, high expression, easy purification of product and wide application range. However, because of the simple cellular anatomy, E.coli has limited ability of post-translational modifications. Sophisticated protein products may suffer from a low biological activity. Besides, insoluble aggregates called inclusion bodies may be formed in cytoplasm due to the incorrect folding of protein, leading to the difficult purification.