Structured Model for Intracellular PHB Production
This Demonstration shows the process of cell growth and synthesis of the intracellular product poly -hydroxybutyric acid (PHB). Residual biomass is the difference between total cell dry mass and product PHB . Synthesis of PHB occurs with a single limiting substrate and constant dissolved gas concentrations of , and .
Reference  presents a structured model for the batch culture of Alcaligenes eutrophus under chemolithoautotrophic growth conditions. Growth and storage of PHB are represented as functions of the concentrations of , the limiting substrate (); , the residual biomass and , the product (PHB).
The whole cell dry mass consists of two main parts, namely PHB () and residual biomass (), where is the difference between the total cell dry weight and the concentration of PHB: . can be considered as the catalytically active biomass, including proteins and nucleic acids. Two distinct phases can be recognized with constant concentrations of the dissolved gases: growth and storage. There is sufficient during the growth phase to permit protein synthesis. Protein synthesis ceases when the limiting substrate is exhausted and the production rate of PHB is increased. Only PHB is produced during the storage phase. The limiting substrate is essential to produce residual biomass and limits its synthesis at low concentrations.
 I. J. Dunn, E. Heinzle, J. Ingham and J. E. Prvenosil, Biological Reaction Engineering, Weinheim, Germany: VCH Verlagsgesellschaft mbH, 2003.