title: Limiting factors in Escherichia coli fed-batch production of recombinant proteins.
abstract: Fed-batch production of recombinant beta-galactosidase in E. coli was studied with respect to the specific growth rate at induction. The cultivations were designed to induce protein production by IPTG at a glucose feed rate corresponding to high mu = 0.5 h(-1)) or low (mu = 0.1 h(-1)) specific growth rate. Protein production rate was approximately 100% higher at the higher specific growth rate, resulting in the accumulation of beta-galactosidase up to 30% of the total cell protein. Transcription analysis showed that beta-galactosidase-specific messenger RNA was immediately formed after induction (<5 min), but the amount was the same in both cases and was thus not the initial limiting factor. The content of ribosomes, as represented by rRNA, rapidly decreased with specific growth rate from a relative level of 100%, at the high specific growth rate, to 20% at the low specific growth rate. At high specific growth rate, ribosomes were additionally degraded upon induction due to the high production level. Translation therefore seemed to be the initial limiting factor of the protein synthesis capacity. The alarmone guanosine tetraphosphate increased at both high and low feed level inductions, indicating an induction-forced starvation of charged tRNA and/or glucose. The altered physiological status was also detected by the formation of acetic acid. However, the higher production rate resulted in high-level accumulation of acetic acid, which was absent at low feed rate production. Acetic acid production is thus coupled to the high product formation rate and is proposed to be due either to a precursor drain of Krebs cycle intermediates and a time lag before induction of the glyoxalate shunt, or to single amino acid overflow, since the model product is relatively poor in glycin and alanin. In conclusion, it is proposed that production at high specific growth rate becomes precursor-limited, while production at low specific growth rate is carbon- and/or energy-limited.
authors.affiliation: The Swedish Centre for Bioprocess Technology, Stockholm Center for Physics, Astronomy and Biotechnology, SE-106 91, Stockholm, Sweden.
authors.forename: Anna Maria
authors.initials: AM
authors.lastname: Sandén
authors.forename: Ingela
authors.initials: I
authors.lastname: Prytz
authors.forename: Ioannis
authors.initials: I
authors.lastname: Tubulekas
authors.forename: Cecilia
authors.initials: C
authors.lastname: Förberg
authors.forename: Ha
authors.initials: H
authors.lastname: Le
authors.forename: Andrea
authors.initials: A
authors.lastname: Hektor
authors.forename: Peter
authors.initials: P
authors.lastname: Neubauer
authors.forename: Zoltan
authors.initials: Z
authors.lastname: Pragai
authors.forename: Colin
authors.initials: C
authors.lastname: Harwood
authors.forename: Alan
authors.initials: A
authors.lastname: Ward
authors.forename: Antonia
authors.initials: A
authors.lastname: Picon
authors.forename: Joost Teixeira
authors.initials: JT
authors.lastname: De Mattos
authors.forename: Pieter
authors.initials: P
authors.lastname: Postma
authors.forename: Anne
authors.initials: A
authors.lastname: Farewell
authors.forename: Thomas
authors.initials: T
authors.lastname: Nyström
authors.forename: Solvejg
authors.initials: S
authors.lastname: Reeh
authors.forename: Steen
authors.initials: S
authors.lastname: Pedersen
authors.forename: Gen
authors.initials: G
authors.lastname: Larsson
mesh_terms: D019342:Acetic Acid / Q000378:metabolism; D001426:Bacterial Proteins / Q000096:biosynthesis*; D003470:Culture Media; D004926:Escherichia coli / Q000235:genetics* / Q000254:growth & development / Q000378:metabolism; D005285:Fermentation; D015870:Gene Expression; D005947:Glucose / Q000378:metabolism*; D007700:Kinetics; D014176:Protein Biosynthesis; D011994:Recombinant Proteins / Q000096:biosynthesis; D014158:Transcription, Genetic; D001616:beta-Galactosidase / Q000096:biosynthesis
chemical_list: D001426:Bacterial Proteins; D003470:Culture Media; D011994:Recombinant Proteins; D001616:beta-Galactosidase; D005947:Glucose; D019342:Acetic Acid