Synthesis Of Citrulline By Immobilized Streptococcus Faecalis

As an ?-amino acid,citrulline has significant physiological functions such as antioxidation,anti-aging,enhancing immunity,improving motor function,vasodilatation,scavenging free radicals and diagnosing rheumatoid arthritis and so on.At present,it has been widely used in food,cosmetics,medicine,environmental protection and energy development.The production methods of citrulline mainly include extraction method,chemical method,fermentation and enzymatic conversion.Enzymatic conversion method which utilizes arginine deiminase in microbial cells to catalyzing and converting L-arginine to L-citrulline,is the most important method and has great research value.In this paper,Streptococcus faecalis BT-13,a mutagenic strain stored in our laboratory,was used to study the optimum process parameters of fermentation and conversion,the best immobilization method and the optimum immobiliz-ation conversion process parameters by using polystyrene-isoprene(SIS)as the carrier.Firstly,effects of fermentation culture conditions on conversion of citrulline by the bacterial were investigated.The results were as follows:the fermentation time is 20 h,inoculation amount 2%,medium volumes 100 ml,pH 6.5,170 rpm,37 ? and add 4%acetone to the fermentation medium.Under these fermentation conditions,40 g·L-1 citrulline was obtained after converting 100 g·L-1 arginine for 24 h.Secondly,the optimum conversion conditions for the production of citrulline by free cells were investigated:40 ml 0.4 mol·L-1 acetic acid buffer,1.6 g wet bacteria as catalyst,substrate arginine concentration 100 g·L-1,CTAB concentration 0.3 g·L-1,pH 6.0,120 rpm,37 ?.Under these conversion conditions,100 g·L-1 arginine can be coverted to 70 g·L-1 citrulline after converting for 30 h.Finally,the optimal immobilization method and optimum conversion process were studied by using polystyrene-isoprene-styrene(SIS)as carrier.The immobilization conditions were as follows:95 ?,20 g SIS carrier,10 mL 18%PVA-1795 aqueous solution,0.1 g Tween-80,2 g PEG-1500.The embedding amount is 4 g wet bacteria,embedding rate is 88.9%.Under these immobilization conditions,the optimum conversion conditions of citrulline were as follows:concentration of arginine was 100 g·L-1,pH 6.5,40 mL 0.2 mol·L-1 acetic acid buffer,0.3 g·L-1 CTAB,100 rpm,37 ?,100 g·L-1 arginine can be coverted to 10 g·L-1 citru-lline after converting for 24 h.Compared with free cells,immobilized cells were more stable and could be used more than 10 batches.