Thermostable arginase from Sulfobacillus acidophilus with neutral pH optimum applied for high-efficiency L-ornithine...

This study aims to use neutral pH optimum arginase as the catalyst for high-efficiency L-ornithine production. Sulfobacillus acidophilus arginase was firstly cloned and overexpressed in Escherichia coli. The purified enzyme was obtained, and the molecular mass determination showed that this arginase was a hexamer. S. acidophilus arginase possessed similarities with the other arginases such as the conserved sequences, purification behavior, and the necessity for Mn²⁺ as a cofactor. The maximum enzyme activity was obtained at pH 7.5 and 70 °C. Thermostability and pH stability analysis showed that the arginase was stable at 30-60 °C and pH 7.0-8.5, respectively. The kinetic parameters suggested that S. acidophilus arginase could efficiently hydrolyze L-arginine. Bioconversion with this neutral pH optimum arginase had the advantages of avoiding producing by-product, high molar yield, and high-level production of L-ornithine. When the bioconversion was performed with a fed-batch strategy and a coupled-enzyme system involving S. acidophilus arginase and Jack bean urease, the final production of 2.87 mol/L was obtained with only 1.72 mmol/L L-arginine residue, and the molar yield was 99.9%. The highest production record suggests that S. acidophilus arginase has a great prospect in industrial L-ornithine production.