title: Metabolic energy-based modelling explains product yielding in anaerobic mixed culture fermentations.
abstract: The fermentation of glucose using microbial mixed cultures is of great interest given its potential to convert wastes into valuable products at low cost, however, the difficulties associated with the control of the process still pose important challenges for its industrial implementation. A deeper understanding of the fermentation process involving metabolic and biochemical principles is very necessary to overcome these difficulties. In this work a novel metabolic energy based model is presented that accurately predicts for the first time the experimentally observed changes in product spectrum with pH. The model predicts the observed shift towards formate production at high pH, accompanied with ethanol and acetate production. Acetate (accompanied with a more reduced product) and butyrate are predicted main products at low pH. The production of propionate between pH 6 and 8 is also predicted. These results are mechanistically explained for the first time considering the impact that variable proton motive potential and active transport energy costs have in terms of energy harvest over different products yielding. The model results, in line with numerous reported experiments, validate the mechanistic and bioenergetics hypotheses that fermentative mixed cultures products yielding appears to be controlled by the principle of maximum energy harvest and the necessity of balancing the redox equivalents in absence of external electron acceptors.
authors.affiliation: Department of Chemical Engineering, Institute of Technology, University of Santiago de Compostela, 15782, Santiago de Compostela, Galicia, Spain.
authors.forename: Rebeca
authors.initials: R
authors.lastname: González-Cabaleiro
authors.affiliation: Department of Chemical Engineering, Institute of Technology, University of Santiago de Compostela, 15782, Santiago de Compostela, Galicia, Spain.
authors.forename: Juan M
authors.initials: JM
authors.lastname: Lema
authors.affiliation: Institute Centre for Water and Environment (iWater), Department of Chemical and Environmental Engineering (CEE), Masdar Institute of Science and Technology, PO Box 54224, Abu Dhabi, United Arab Emirates.
authors.forename: Jorge
authors.initials: J
authors.lastname: Rodríguez
mesh_terms: D000693:Anaerobiosis; D001673:Biodegradation, Environmental; D001693:Biological Transport, Active; D019149:Bioreactors / Q000382:microbiology*; D004579:Electron Transport; D005285:Fermentation; D005561:Formates / Q000378:metabolism; D005947:Glucose / Q000378:metabolism; D006859:Hydrogen / Q000378:metabolism; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D053858:Metabolic Networks and Pathways; D008954:Models, Biological
chemical_list: D005561:Formates; C030544:formic acid; D006859:Hydrogen; D005947:Glucose