Extracellular expression of natural cytosolic arginine deiminase from Pseudomonas putida and its application in the production of l-citrulline

The Pseudomonas putida arginine deiminase (ADI), a natural cytosolic enzyme, and Thermobifida fusca cutinase were co-expressed in Escherichia coli, and the optimized cutinase gene was used for increasing its expression level. 90.9% of the total ADI protein was released into culture medium probably through a nonspecific leaking mechanism caused by the co-expressed cutinase. The enzymatic properties of the extracellular ADI were found to be similar to those of ADI prepared by conventional cytosolic expression. Extracellular production of ADI was further scaled up in a 3-L fermentor. When the protein expression was induced by IPTG (25.0 μM) and lactose (0.1 g L−1 h−1) at 30 °C, the extracellular ADI activity reached 101.2 U mL−1, which represented the highest ADI production ever reported. In addition, the enzymatic synthesis of l-citrulline was performed using the extracellularly expressed ADI, and the conversion rate reached 100% with high substrate concentration at 650 g L−1.