Overexpression of streptokinase using a fed-batch strategy

The structural gene for streptokinase was cloned under the T7 promoter cont aining the ompA secretory signal sequence. The T7 RNA polymerase was induce d with IPTG when the biomass concentration was 1.2 mg dry cells/ml and puls e feeding of concentrated substrate was done at different time intervals. T he biomass concentration reached 1.8 mg dry cells/ml and the activity obtai ned in the supernatant was 180 plasmin units/ml compared to 17 plasmin unit s/ml obtained by growing and inducing the cells in simple LB medium. The re sults indicate that high expression levels can be obtained with high cell d ensity cultivation in the T7 system by using a proper feeding strategy.