Enhancement of l-amino acid oxidase production by Bacillus subtilis HLZ-68 with oxygen-vector and asymmetric degradation of dl-arginine to d-arginine

Abstract

Bacillus subtilis HLZ-68 can produce l-amino acid oxidase (l-AAO), and dl-arginine can be degraded asymmetrically by suspending the wet bacterial biomass in the degradation liquid. By adding oxygen-vectors to the fermentation medium, the collected amount of wet bacterial biomass can be increased. Taking n-dodecane, n-hexadecane, oleic acid, paraffin and n-hexane as oxygen-vectors, the optimal oxygen-vector was 1.2% (v/v) oleic acid. The wet weight biomass increased by 66.83% and the activity of l-AAO in the fermentation broth increased by 38.88% compared with those before the addition of oxygen-vector. The standard sample dl-arginine was derivatized by phenyl isothiocyanate, and then subjected to high-performance liquid chromatography (HPLC), and the obtained peak area and arginine content were used as standard curves to measure the dl-arginine. The content of d-arginine and l-arginine in the initial degradation solution was 50% each, and the bacterial cells were added to the initial degradation solution of dl-arginine. After 21 h of reaction, l-arginine was completely degraded, leaving 47% of d-arginine. d-alanine was easily extracted from the reaction solution using cation-exchange resin, after centrifugation, decolourization, concentration and vacuum drying, and the chemical and optical purity of the extracted d-arginine were 92.68% and 97.46%, respectively.