Dynamics of single-substrate continuous cultures: An integrated model of bacterial cell

COMP 155

Shakti Gupta, SGupta4@cdc.gov, National Center for Infectious Diseases, Centers for Disease Control and Prevention, Atlanta, GA 30333, Sergei S. Pilyugin, Department of Mathematics, University of Florida, Gainesville, FL 32611, and Atul Narang, Department of Chemical Engineering, University of Florida, Gainesville, FL 32611.
When a chemostat is perturbed from its steady state, it displays complex dynamics. For instance, if the identity of the growth-limiting substrate is switched abruptly, the substrate concentration and cell density undergo a pronounced excursion from the steady state that can last several days. These dynamics occur because certain physiological variables respond slowly. In the literature, several physiological variables have been postulated as potential sources of the slow response. These include the transport enzyme, the ribosomes, and the concentrations of adenine nucleotides. The goal of this work is to systematically explore the relative role of these variables. We studied the role of transport enzymes by describing experiments in which low levels of the transport enzyme limits growth. It was shown that the long lags occur because transport enzyme synthesis is autocatalytic. A model was developed accounting the transport enzyme synthesis, which can capture these experimental data quantitatively. We extended the model by describing experiments in which the lags persist even if the transport levels are high. In this case, the growth rates appear to be limited by the protein synthetic machinery (ribosomes). An extended model taking due account of ribosomes synthesis can capture these observed transients qualitatively. Since the cell consumes the substrate, but is unable to convert it to proteins effectively. The excess substrate in the cell is thus discharged as partially oxidized metabolites. We have further extended the model by incorporation of the energy balance, which constrains the relative rates of protein synthesis, metabolite excretion, and respiration.

Poster Session -- Sponsored by Novartis Institutes for BioMedical Research
6:00 PM-8:00 PM, Tuesday, 30 August 2005 Washington DC Convention Center -- Hall A, Poster

8:00 PM-10:00 PM, Monday, 29 August 2005 Washington DC Convention Center -- Hall A, Sci-Mix

Division of Computers in Chemistry

The 230th ACS National Meeting, in Washington, DC, Aug 28-Sept 1, 2005