Effect Of Oxygen-vectors On Bacillus Fermentation And Production Of D-arginine By Asymmetric Degradation

As an important chiral compound,D-arginine is used in many fields such as medicine,food and agriculture,but it is not widely distributed in nature.At present,the D-arginine market is expensive.In this study,the strain Bacillus subtilis cells were obtained from Guangxi University,and it can produce D-arginine from DL-arginine by asymmetric degradation.There are two main factors affecting the production of D-arginine by asymmetric degradation of wet cells:less wet cells and lower enzyme activity.Therefore,there is an urgent need to develop a simple and efficient method to production D-arginine.By adding an oxygen carrier to the initial fermentation broth,the amount of wet cells collected is increased.In this study,different compounds such as n-dodecane,n-hexadecane,oleic acid,paraffin,and n-hexane as the oxygen carrier,the optimal oxygen carrier oleic acid was 1.2%（v/v）.The weight of wet cells increased by 66.83%.Through single factor method and response surface design are used to optimize inorganic salt ions.The inorganic salt ions were as follows:KH₂PO₄addition amount 6 g/L,K₂HPO₄addition amount 3 g/L,Mg SO₄·7H₂O addition amount 3.6 g/L,Ca Cl₂addition amount 0.11 g/L,Zn SO₄addition amount 0.6 g/L,Mn SO₄addition amount 0.04 g/L,H₃BO₃addition amount 0.2 g/L.Under this condition,the enzyme activity was 110.96 U/g,which was 117.14%higher than that of 51.1 U/g before optimization.The degradation conditions were optimized by single factor and orthogonal experiment.The optimum degradation conditions were as follows:reaction solution volume 50/250 m L,degradation temperature 30℃,substrate concentration 40 g/L,wet cells 40 g/L,speed 240r/min,p H 6.0.Under these conditions,the enzyme activity reached to 220.3U/g and were improved 98.54%than before.Addition of 270 g of DL-arginine（180 g at the beginning of the reaction and 90 g after 9h of incubation）into the reaction solution resulted in complete L-arginine degradation within30 h,leaving 130 g of D-arginine in the reaction solution.The degradation solution was centrifuged,decolorized,concentrated,and crystallized.The total recoveries of D-arginine were 91.58%,the transmittance was more than 95%,the chemical and optical purity of the obtained D-arginine was 92.68%and 97.46%.This experiment reached the goal of producing high-purity D-arginine,indicating that the production of D-arginine by asymmetric degradation has great application value,and laid a good foundation for the industrial production of D-arginine.