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Title: The effect of imperfect mixing on the performance of Escherichia coli K12
Author: Oxbek, B.
Awarding Body: University College of Swansea
Current Institution: Swansea University
Date of Award: 1993
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The facultative anerobic nature of Escherichia coli allows the study of the effects of oxygen on growth, metabolism and enzyme expression in a deliberately poorly mixed fermentation system that mimic conditions found in industrial fermenters. A methionine auxotroph of Escherichia coli, NCIMB 9481, grown on a defined medium, was used to investigate scale-down fermentations. Two approaches were taken to investigate this problem. The first involved the construction, characterisation and operation of a laboratory fermentation system. The continuous fermentation system consisted of a 2 L stirred tank reactor (CSTR) which is linked to a 0.5 L recirculating plug flow tubular reactor (PFTR). The second approach involved the development of a general mathematical model to describe the growth of Escherichia coli in the combined system (CSTR + PFTR). The model based on Monod kinetics, took into account the mixing environment in the reactor and was able to predict the oxygen sensitive substrate (glucose) consumption, endogenous metabolism, biomass formation, metabolic end-product formation (ethanol, acetic acid and carbon dioxide), and the expression of the malate dehydrogenase enzyme. The growth of Escherichia coli in the combined system and its physiological response to variations in recirculation rate, aeration rate, initial substrate concentration were then investigated. These results, when compared with those predicted by the simulation, demonstrated that the model gave an accurate prediction of microbial product formation with the exception of the metabolic end-products. Simulations were then used to explore the mixing characteristics of the combined system. In particular the response of the microbe to mixing as expressed by the volume fraction (εT), (VPFTR/(VPFTR+ VCSTR)), and the recirculation ratio (R). The results show that εT significantly effects the performance of Escherichia coli. The recirculation ratios (R) only effect the system at high dilution rates where system deviates from CSTR mixing theory.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available