The pathway of poly-beta-hydroxybutyric acid (PHB) exhibits a mode of transcriptional control induced by environmental stress. A new cybernetic model for coordinated regulation of stress-induced metabolism was developed to predict the growth and the synthesis of PHB in Alcaligenes eutrophus. A plausible objective for this control is optimization of acetyl-CoA utilization so that the cells have a high degree of flexibility in their catabolism. The state equation for key protein synthesis was assumed to have a dependence on the nonlinear control variable. The proposed model can demonstrate the mixed-growth-associated synthesis of PHB. Reported unstructured models were compared statistically with the result of the simulation derived from the proposed model using the experimental data of this study and the literature. The proposed model appeared to provide an excellent description for the overall fermentation rage.