title: Impact of dissolved hydrogen partial pressure on mixed culture fermentations.
abstract: Mixed culture fermentations are of interest for the low-cost production of organic acids from complex agricultural waste streams. Models are developed for these processes in order to predict the product spectrum as a function of the environmental process conditions. An important assumption in many existing models for anaerobic mixed culture fermentations is that the NADH/NAD(+) ratio is directly coupled to the dissolved hydrogen partial pressure (pH2, liquid). In this study, this assumption was tested experimentally with mixed culture chemostats operated at dilution rates of 0.05 and 0.125 h(-1) for a wide range of calculated dissolved hydrogen partial pressures (0.04-6.8 atm). No correlation was found between pH2, liquid and the NADH/NAD(+) ratio. This result, together with thermodynamic calculations, suggests that additional electron carriers such as ferredoxin and formate should be included in models predicting product formation by mixed cultures.
authors.affiliation: Department of Biotechnology, Delft University of Technology, Julianalaan 67, 2628 BC, Delft, The Netherlands. stefandekok@gmail.com
authors.forename: Stefan
authors.initials: S
authors.lastname: de Kok
authors.forename: Jasper
authors.initials: J
authors.lastname: Meijer
authors.forename: Mark C M
authors.initials: MC
authors.lastname: van Loosdrecht
authors.forename: Robbert
authors.initials: R
authors.lastname: Kleerebezem
mesh_terms: D001421:Bacteria, Anaerobic / Q000254:growth & development / Q000378:metabolism*; D002264:Carboxylic Acids / Q000378:metabolism*; D003470:Culture Media / Q000737:chemistry*; D005285:Fermentation; D006859:Hydrogen / Q000378:metabolism*; D007218:Industrial Microbiology / Q000379:methods*; D017744:Medical Waste Disposal / Q000379:methods*; D009243:NAD / Q000032:analysis; D010313:Partial Pressure; D013816:Thermodynamics
chemical_list: D002264:Carboxylic Acids; D003470:Culture Media; D017744:Medical Waste Disposal; D009243:NAD; D006859:Hydrogen