APPLICATION OF BIOENERGETIC PRINCIPLES TO MODELLING THE BATCH FERMENTATION OF D-XYLOSE TO 2,3-BUTANEDIOL BY KLEBSIELLA PNEUMONIAE
Abstract
Klebsiella pneumoniae ferments a variety of pentose and hexose sugars to 2,3-butanediol. Butanediol may be a valuable chemical feedstock that can be converted to methyl ethyl ketone or 1,3-butadiene. Butanediol production from D-glucose has been previously examined. The purpose of this research is to investigate the batch kinetics of this fermentation where D-xylose is the sole carbon and energy source, and to develop a predictive model simulating butanediol production. Experiments investigating this fermentation reveal that the optimum pH is in the range pH 5.2-5.6. Batch fermentation yields and rates depend strongly on the oxygen transfer rate and the initial substrate concentration. A mathematical model simulating the effects of these two variables on kinetics is developed using macroscopic material balance and bioenergetic principles. K. pneumoniae is a facultative anaerobe which obtains all the energy it needs by two different energy producing pathways. During oxygen limited growth, both pathways are active simultaneously. Butanediol is a product of one of these pathways. The model that is developed is able to predict butanediol production by writing an ATP balance equating the ATP produced by the two energy producing pathways to the ATP required for growth and maintenance of viability. The ATP produced can be calculated from the known stoichiometry of the catabolic pathways. The ATP consumed is assumed to consist of a growth associated component and a non-growth (or maintenance) component. Two bioenergetic parameters are used to quantify this ATP requirement. They are the maximum cell yield from ATP, and the maintenance energy requirement. This ATP requirement is assumed to determine the extent to which the energy producing reactions occur. The resulting model requires only four independent parameters. Values of the three bioenergetic parameters are inferred from batch fermentation data. A product inhibition parameter is determined from shake flask and fed-batch fermentations. The model accurately predicts variations in the final butanediol yield and butanediol production rate as functions of both the oxygen supply rate and xylose concentration.
Degree
Ph.D.
Subject Area
Chemical engineering
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