L-phenylacetylcarbinol(L-PAC),an important organic synthesis intermediate,is used as a precursor of L-ephedrine and D-pseudo-ephedrine in the pharmaceutical industry.L-PAC is also used for synthesis of drugs of amphetamine,amphetamine and aniline.There are some obstacles for whole-cell microbial transformation of benzaldehyde into L-PAC,mainly including the toxic effect of substrate/product to microorganism.Extractive microbial transformation is a potential tool to eliminate the product inhibition.However,a whole cell microbial transformation of a moderate polar substrate/product in an organic solvent-water two-phase partitioning system is usually difficult for selection of an appropriate organic solvent as maintenance of the microbial cell activity and an extraction of the moderate polar substrate/product into the organic solvent phase can not be fulfilled at the same time.When temperature is higher than the cloud point temperature of a nonionic surfactant solution,the nonionic surfactant aqueous solution will automatically form a dilute phase with a little of surfactant and a coacervate phase containing most of the surfactant.This system is called a cloud point system.The biocompatibility of cloud point system was studied by comparing the cloud point system and dispersed surfactant system in Triton X-45-Triton X-114 mixture nonionic surfactant aqueous system.A polyethylene glycol(PEG)induced cloud point system was further developed to extract the moderate polar product in the microbial transformation process.Extractive microbial transformation of benzaldehyde into L-PAC by whole cell Saccharomyces cerevisiae was optimized in the polyethylene glycol PEG-induced cloud point system.The PEG-induced cloud point system is composed of 80 g PEG 20000,75 ml Triton X-100,20 g peptone,10 g yeast extract,25 g glucose,1 g MgSO4·7H2O,0.05 g CaCl2·2H2O,35 g Na2HPO4·12H2O,and 10.7 g citric acid in every liter of tap water.The microbial transformation is conducted with 0.6 ml of acetaldehyde(35%volume content), 0.9 ml of benzaldehyde and 7 g of wet cell in per 100 ml of the PEG-induced cloud point system.Under the optimal condition,a relatively longer time of whole cell microorganism bioactivity had been achieved.A high final product concentration to about 8 g/l was achieved by fed-batch microbial transformation process with a discrete addition of glucose and substrate.It indicates that the PEG induced cloud point system may be a potential technique for in situ removal of a relatively higher polar product in a whole cell microbial transformation process. |