Metabolic flux analysis for anaerobic mixed-cultural fermentation systems

Abstract

As the global warming and energy crisis become serious and unneglectable bioenergies production for wastewater treatment via anaerobic digestion poses an alternative options Anaerobic digestion could potentially produce H2 ethanol butanol CH4 and other volatile fatty acids from organic wastewaters however difficulties remain to produce pure product or even to enhance the yield due to the complex metabolic network in anaerobic digestion Until now developing a tool to describe or even to control the complex flux distribution between various metabolites during anaerobic digestion is still an unsolved task making anaerobic digestion an unstable and hardly applicable process for wastewater treatment Metabolic flux analysis (MFA) is a method based on stoichiometry and mass balance which was mostly used for metabolic engineering with pure culture system In this study a mixed-cultural metabolic network for anaerobic digestion was constructed by involving the concept of “universal bacterium” and the proposed network was used for MFA to evaluate the electron and material flows during different anaerobic processes under various conditions The mixed-cultural metabolic network consisting of glycolysis pentose phosphorylation pathway (PPP) lactate branch acetyl-CoA branches (including acidogenesis and solventogenesis) TCA cycle and post-acidogenesis branches (such as acetogenesis and methanogenesis was successfully applied to MFA using the results from H2 bioreactors acetone-butanol-ethanol fermentative bioreactors acetogenesis bioreactors and methanogenesis bioreactors Results obtained from the MFAs applying to H2 bioreactors fed with cellulose lactate and acetate and three different types of bioethanol fermented residues showed that PPP lactate branch and TCA cycle are important to regulate NADH and could potentially affect H2 production Pearson’s correlation analysis shows that the flux of H2 production had positive correlations with the reduction of ferredoxin with pyruvate oxidation acetate formation and its emission when lactate was produced in the system while negative relationships were found between the flux of H2 production and these three fluxes Results of MFA from ABE bioreactors indicate that the flux toward butanol increased with decreasing fluxes for acetate and butyrate while batch experiments also show the addition of butyrate could enhance butanol yield The MFA results of two bioreactors for acetogenesis from H2/CO2 indicate that PPP is an important flux since its negative flux acted as a CO2 sink leading to ATP production in glycolysis which could be used in Wood-Ljungdahl pathway the conversion of H2 and CO2 to acetyl-CoA During the investigation of CH4 bioreactor MFA result successfully identified and described the dominance shift between hydrogenotrophic methanogenesis and aceticlastic methanogenesis

Date of Award	2019
Original language	English
Supervisor	Liang-Ming Whang (Supervisor)