Cybernetic modeling of microbial growth on substitutable substrates: Applications in bioremediation

Ramprasad Ramakrishna, Purdue University

Abstract

Growth of microorganisms on substitutable substrate mixtures display diverse growth dynamics characterized by simultaneous or preferential uptake of carbon sources. The development of models for microbial growth differ from standard reaction engineering approaches due to the ability of microorganisms to regulate their metabolism. The cybernetic framework, by recognizing the optimal nature of microbial growth provides a versatile alternative to more complex kinetic models. A significant feature of the framework is the representation of the control of synthesis and activities of enzymes and the importance of the rates of the processes they catalyze on this regulation through the formulation of cybernetic variables. A cybernetic model which recognizes the importance of the synthesis of biosynthetic precursors in cell growth through a kinetic structure that is quite general for any mixture of carbon-energy sources has been developed. The growth of Escherichia coli on mixtures of glucose and organic acids such as pyruvate, fumarate and succinate have been described successfully by the model. Both preferential and simultaneous uptake patterns are predicted and the model also describes the changes in utilization patterns that occur under changing substrate concentrations, modes of preculturing and in continuous cultures with changes in dilution rates. The model has been applied to characterizing the substrates-species interactions under the influence of growth rate. A hypothetical representation of this relationship based on a general paradigm for resource classification is proposed. This representation is verified using the cybernetic model and the results show that for the same pair of carbon sources the qualitative nature of the "consumer-resource" relationship changes with changing specific growth rate. This result is of significance in the area of microbial ecology. Experimental investigations on the bacterial metabolism of naphthalene in the presence of other carbon sources are presented. The growth patterns observed show the same trends as the studies with E. coli. These experiments suggest strategies for bioremediation based on the addition of suitable supplementary substrates. The model was applied to simulate the results of these strategies and the simulations show that biodegradation can be enhanced by optimal addition of supplementary substrates.

Degree

Ph.D.

Advisors

Ramkrishna, Purdue University.

Subject Area

Chemical engineering

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