E.coli is one of the most widely used and well-studied expression systems. This system is excellent for expression of functional non-glycosylated proteins, since the production of glycosylated proteins require a Golgi apparatus, which E. coli cells do not posses. Bacteria did not develop a sophisticated mechanism for performing posttranslational modifications. The following table summarizes the advantages and disadvantages of E.coli as an expression system.

Advantages Disadvantages
Rapid expression Protein with disulfide bonds is difficult to express
High yield Produces unglycosylated proteins
Ease of culture and genome modification Protein produced with endotoxin
Inexpensive Acetate formation resulting in cell toxicity
Mass production is fast and cost-effective Protein produced as inactive inclusion bodies that require refolding

Figure 1. Bacteria expression system.