title: Formate as an auxiliary substrate for glucose-limited cultivation of Penicillium chrysogenum: impact on penicillin G production and biomass yield.
abstract: Production of beta-lactams by the filamentous fungus Penicillium chrysogenum requires a substantial input of ATP. During glucose-limited growth, this ATP is derived from glucose dissimilation, which reduces the product yield on glucose. The present study has investigated whether penicillin G yields on glucose can be enhanced by cofeeding of an auxiliary substrate that acts as an energy source but not as a carbon substrate. As a model system, a high-producing industrial strain of P. chrysogenum was grown in chemostat cultures on mixed substrates containing different molar ratios of formate and glucose. Up to a formate-to-glucose ratio of 4.5 mol.mol(-1), an increasing rate of formate oxidation via a cytosolic NAD(+)-dependent formate dehydrogenase increasingly replaced the dissimilatory flow of glucose. This resulted in increased biomass yields on glucose. Since at these formate-to-glucose ratios the specific penicillin G production rate remained constant, the volumetric productivity increased. Metabolic modeling studies indicated that formate transport in P. chrysogenum does not require an input of free energy. At formate-to-glucose ratios above 4.5 mol.mol(-1), the residual formate concentrations in the cultures increased, probably due to kinetic constraints in the formate-oxidizing system. The accumulation of formate coincided with a loss of the coupling between formate oxidation and the production of biomass and penicillin G. These results demonstrate that, in principle, mixed-substrate feeding can be used to increase the yield on a carbon source of assimilatory products such as beta-lactams.
authors.affiliation: Delft University of Technology, Department of Biotechnology, Julianalaan 67, Delft, The Netherlands.
authors.forename: Diana M
authors.initials: DM
authors.lastname: Harris
authors.forename: Zita A
authors.initials: ZA
authors.lastname: van der Krogt
authors.forename: Walter M
authors.initials: WM
authors.lastname: van Gulik
authors.forename: Johannes P
authors.initials: JP
authors.lastname: van Dijken
authors.forename: Jack T
authors.initials: JT
authors.lastname: Pronk
mesh_terms: D000332:Aerobiosis; D018533:Biomass; D001709:Biotechnology / Q000379:methods*; D003470:Culture Media; D005561:Formates / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D010400:Penicillin G / Q000378:metabolism*; D010408:Penicillium chrysogenum / Q000254:growth & development* / Q000378:metabolism; D047090:beta-Lactams / Q000378:metabolism
chemical_list: D003470:Culture Media; D005561:Formates; D047090:beta-Lactams; D005947:Glucose; D010400:Penicillin G