CHARACTERIZATION OF THE GROWTH DYNAMICS AND DEVELOPMENT OF A MECHANISTIC MODEL OF A METHANOL-UTILIZING BACTERIUM
Abstract
A set-point-controlled two fermentor setup (SPC-controlled TFS) was built as a part of a general hierarchical micro-minicomputer fermentor network (Hi MiMiC Fermwork). The SPC-controlled TFS was used to study the growth dynamics of a methanol utilizing bacterium (L3). The study included batch, continuous culture startup and transient relaxation, and perturbed continuous growth experiments. The batch growth dynamics of L3 was characterized by the presence of unbalanced and balanced growth phases, whereas the continuous growth dynamics was categorized as growth under carbon limited (C(,lim)) and carbon excess (C(,exs)) conditions. The experimental findings of diverse dynamic growth of L3 were also characterized by the presence of growth and product rate hystereses, asymmetric multilevel dynamic responses, multiple non-trivial steady states, and bifurcating oscillatory growth pattern. The diversity of dynamic growth was ascribed to the existence of C(,lim) and C(,exs) growth conditions in fermentors. Based on the biochemical knowledge of methanol utilizing microorganisms and current knowledge of the isolate L3, a non-segregated mechanistic model was developed. Structure in the model was classified as basic structure and regulatory structure. The basic structure was developed in three steps: (a) preliminary analysis of an unstructured model, (b) incorporation of formaldehyde as a state variable, and (c) inclusion of a 'pump-and-leak' mechanism of formaldehyde transport. The development of regulatory structure was also accomplished in three steps: (a) incorporation of growth inhibition due to formaldehyde, (b) inclusion of a complex inhibition of methanol oxidation by formaldehyde, and (c) admission of the bottleneck effect. The mechanistic model can adequately describe: (a) the stable steady state and batch growth of L3 on methanol and mixtures of methanol and formaldehyde, (b) the unstable steady state growth of L3, and (c) the fast continuous growth transients quantitatively and the slow transients qualitatively.
Degree
Ph.D.
Subject Area
Chemical engineering
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