Zahra Rastian - Chem. Eng. Dept., IUST, Narmak, Tehran
Fereshteh Naeimpoor - Chem. Eng. Dept., IUST, Narmak, Tehran

While cells grow, biosynthesis is the most important part of the cell metabolism, however, as part of necessary steps for existence, some cell components are degraded after synthesis. Therefore, cell components are microscopically in a dynamic state while macroscopically could be in a static state. Even for bacteria in balanced, exponential growth some substances, under some conditions, are turned over and re-synthesized again. Maintenance energy is used to lump the effect of all un-known or un-modeled cell functions, such as turnover, in cell behavior. In this study, turnover of cell components is modeled and excluded from maintenance energy. Using metabolic flux analysis (MFA), the effects of maintenance energy and macromolecule turnover on the maximum specific growth rate of streptomyces are investigated. Theoretical evaluations show that by increasing maintenance energy the specific growth rate decreases. Incorporation of protein, RNA and DNA turnover in the metabolism results in reduction of specific growth rate, though the percentage of this reduction depends on the type of macromolecule and its composition in the biomass. Contribution of turnover in maintenance energy is also estimated.

MFA, maintenance energy, turnover, streptomyces