This works presents the development of a minimal parameter first-principle process model for the production of streptokinase using a recombinant E. Coli in a fed-batch reactor. The minimal parameter models are obtained by model-reduction from the complex primary model. The model-reduction was done based on a parameter sensitivity analysis. The observer for predicting the immeasurable internal states online like specific growth rate, specific uptake of alkaline species (Ammonium) , and specific production of acidic species (acetic acid) are developed, using the online measurements of exit gas (CO 2 & O2),Dissolved Oxygen (PO2) and Alkali dosed and the substrate feed rate. The state estimation using an Extended Kalman Filter (EKF) and filter based on spline interpolation using Stirlings formula are presented.