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Physiology and kinetics of cellulose fermentation by Clostridium thermocellum / by Evert K. Holwerda

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Author	Holwerda, Evert K.
Title	Physiology and kinetics of cellulose fermentation by Clostridium thermocellum / by Evert K. Holwerda
Date	2013
Abstract	Cellulolytic microorganisms hold promise for industrially applied microbial cellulose utilization in the generation biofuels from renewable resources. Consolidated bioprocessing (CBP), a one-step process combining cellulase production, cellulose hydrolysis and fermentation to produce biofuels, is viewed as a low cost configuration for processing cellulosic biomass. The thermophilic anaerobe Clostridium thermocellum is a model CBP organism as it can solubilize cellulose into soluble sugars with an extracellular multi-enzyme complex called the cellulosome, and ferment these cellodextrins into ethanol. One of the main constraints to the further application of C. thermocellum as a CBP candidate is the lack of suitable methods required to improve the physiological understanding of microbial cellulose utilization. This thesis focuses on the development and application of methods to study cellulose utilization by C. thermocellum. Methods based on on-line data and elemental analysis in combination with a low-carbon growth medium showed that C. thermocellum grows differently on solid substrate. Comparing batch cultures on cellobiose and on cellulose demonstrated that there is no exponential growth on cellulose, and the specific growth rate on cellulose is never constant and transiently exceeds that of cellobiose. The kinetics of substrate utilization by cellulolytic microorganism have been described in literature by first order in cells and first order in substrate, but these are mutually exclusive. A comparison of different kinetic models showed that the kinetics of batch cellulose utilization are best described by first order in cells and substrate, second order overall. Exploring high substrate loadings showed that C. thermocellum is able to utilize cellulose at industrially relevant concentrations. During batch fermentations of 100 g/L cellulose C. thermocellum stopped growing at 50% conversion, but continued to actively utilize the substrate. The formation of higher alcohols and high amounts of free amino acids ind
Description	xiii, 190 leaves : ill. (some color) 28 cm.
Format	application/pdf
Advisor	Lee R. Lynd, Karl E. Griswold, Jack T. Pronk, Xiongjun Shao, Paul J. Weimer
College	Thayer School of Engineering.
Issuing Body	Dartmouth Dissertations are made available through the Dartmouth Digital Library.
Degree	Thesis (Ph.D.)--Dartmouth College.
Copyright	All rights reserved. No part of this book may be reproduced in any form by any electronic or mechanical means without permission in writing from the author.
DOI	http://dx.doi.org/10.1349/ddlp.969

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