Continuous production of succinic acid by Actinobacillus succinogenes : steady state metabolic flux variation

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dc.contributor.advisor Nicol, Willie
dc.contributor.postgraduate Bradfield, M.F.A. (Michael Ford Alexander)
dc.date.accessioned 2014-07-17T12:10:27Z
dc.date.available 2014-07-17T12:10:27Z
dc.date.created 2014-04-08
dc.date.issued 2013 en_US
dc.description Dissertation (MEng)--University of Pretoria, 2013. en_US
dc.description.abstract Continuous fermentations were performed in a novel external-recycle, biofilm reactor using D-glucose and CO2 as carbon substrates. Corn steep liquor (CSL) and yeast extract (YE) served as nitrogen sources. In anaerobic fermentations using medium containing CSL and YE, succinic acid (SA) yields were found to be an increasing function of glucose consumption. The ratio of SA to the major by-product, acetic acid (YAASA), increased from 2.4 g g-1 at a glucose consumption of 15 g L-1, to 5.7 g g-1 at a glucose consumption of 46 g L-1. For medium containing no CSL, YAASA remained near 1.97 g g-1, exceeding this for cases where biofilm grown on CSL-containing medium was present. The ratio of formic acid to acetic acid (YAAFA), for CSL-containing medium, decreased from an equimolar value (0.77 g g-1) at a glucose consumption of 10 g L-1 to zero at 46 g L-1 glucose consumed. In contrast, YAAFA for YE-only medium remained at 0.77 g g-1. Therefore, pyruvate was metabolised solely by pyruvate-formate lyase when no CSL was present. The highest SA yield obtained on glucose, SA titre and SA productivity were 0.91 g g-1, 48.5 g L-1 and 9.4 g L-1 h-1, respectively, all for medium containing CSL. Medium that included CSL significantly outperformed medium that excluded CSL, achieving 64%, 21% and 203% greater SA titres, yields on glucose and productivities respectively. Metabolic flux analyses based on the established C3 and C4 metabolic pathways of Actinobacillus succinogenes revealed that the increase in YAASA, for CSL-containing fermentations, could not be attributed to the decrease in formate and biomass formation, and that an additional source of reducing power was present. The fraction of reducing power (NADH) unaccounted for increased with glucose consumption, suggesting that the maintenance or non-growth metabolism encountered at higher SA titres differs from the growth metabolism. It is postulated that the additional reducing power originates from an active pentose phosphate pathway in non-growing cells or from an undetected component(s) in the fermentation medium. No major metabolic flux variations were found in fermentations that excluded CSL. en_US
dc.description.availability unrestricted en_US
dc.description.department Chemical Engineering en_US
dc.description.librarian gm2014 en_US
dc.identifier.citation Bradfield, MFA 2013, Continuous production of succinic acid by Actinobacillus succinogenes : steady state metabolic flux variation, MEng dissertation, University of Pretoria, Pretoria, viewed yymmdd <http://hdl.handle.net/2263/40826> en_US
dc.identifier.other E14/4/286/gm en_US
dc.identifier.uri http://hdl.handle.net/2263/40826
dc.language.iso en en_US
dc.publisher University of Pretoria en_ZA
dc.rights © 2013 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria. en_US
dc.subject Actinobacillus succinogenes en_US
dc.subject Biofilm en_US
dc.subject Corn steep liquor en_US
dc.subject Metabolic flux analysis en_US
dc.subject Succinic acid en_US
dc.subject UCTD en_US
dc.title Continuous production of succinic acid by Actinobacillus succinogenes : steady state metabolic flux variation en_US
dc.type Dissertation en_US


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