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

dc.contributor.advisorNicol, Willie
dc.contributor.emailmichael.bradfield@tuks.co.zaen_US
dc.contributor.postgraduateBradfield, M.F.A. (Michael Ford Alexander)
dc.date.accessioned2014-07-17T12:10:27Z
dc.date.available2014-07-17T12:10:27Z
dc.date.created2014-04-08
dc.date.issued2013en_US
dc.descriptionDissertation (MEng)--University of Pretoria, 2013.en_US
dc.description.abstractContinuous 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.availabilityunrestricteden_US
dc.description.departmentChemical Engineeringen_US
dc.description.librariangm2014en_US
dc.identifier.citationBradfield, 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.otherE14/4/286/gmen_US
dc.identifier.urihttp://hdl.handle.net/2263/40826
dc.language.isoenen_US
dc.publisherUniversity of Pretoriaen_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.subjectActinobacillus succinogenesen_US
dc.subjectBiofilmen_US
dc.subjectCorn steep liquoren_US
dc.subjectMetabolic flux analysisen_US
dc.subjectSuccinic aciden_US
dc.subjectUCTDen_US
dc.titleContinuous production of succinic acid by Actinobacillus succinogenes : steady state metabolic flux variationen_US
dc.typeDissertationen_US

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