National Institute of Genetic Engineering and Biotechnology of IranIranian Journal of Biotechnology1728-30439420111001Flux distribution in Bacillus subtilis: inspection on plurality of optimal solutions2602667148ENEhsan MotamedianBiotechnology Research Laboratory, School of Chemical Engineering, Iran University of Science and Technology, P.O. Box 16846-13114, Tehran, I.R. Iran.0000-0001-8750-2879Fereshteh NaeimpoorBiotechnology Research Laboratory, School of Chemical Engineering, Iran University of Science and Technology, P.O. Box 16846-13114, Tehran, I.R. Iran.Journal Article20111001Linear programming problems with alternate solutions are challenging due to the choice of multiple strategies<br />resulting in the same optimal value of the objective function. However, searching for these solutions is a<br />tedious task, especially when using mixed integer linear programming (MILP), as previously applied to<br />metabolic models. Therefore, judgment on plurality of optimal metabolic flux distributions (solutions) a priori<br />to applying MILP approach could prevent unnecessary computations. In this work for the first time, the<br />reduced cost coefficients for the non-basic variables in a current solution of a metabolic model were utilized to<br />inspect the possibility of multiple optimal flux distributions. If there exists at least one non-basic variable<br />with zero reduced cost coefficient, multiplicity of optimal solution may occur where MILP can be used to<br />find these solutions. This approach was implemented on a metabolic network of Bacillus subtilis aiming to<br />reduce the cell energy requirement. Solving the model at fixed specific growth rate of 0.4 1/h resulted in minimum energy requirement of 12.67 mmol/g-h. Inspection of reduced cost coefficients showed that six<br />non-basic variables had zero reduced cost coefficients at current solution, which shows that there can exist<br />multiple optimal solutions. Subsequently, by applying MILP, five optimal flux distributions at minimized energy requirement were identified, among which one showing no acid production and minimum glucose<br />consumption rate was selected as the superior solution.<br /><br />https://www.ijbiotech.com/article_7148_45574c4a50e0842bd9e47df5bcadac12.pdf