Phosphate limited fed-batch processes: impact on carbon usage and energy metabolism in Escherichia coli.
Phosphate starvation is often applied as a tool to limit cell growth in microbial production processes without hampering carbon and/or nitrogen supply alternatively. This contribution focuses on the interplay of process induced phosphate starvation and microbial performance studying an l-tryptophan overproducing Escherichia coli strain as a model for highly ATP demanding processes in comparison with an E. coli wildtype strain. To enable a time-resolved analysis, constant phosphate feeding strategies were applied to elongate the transition from phosphate saturated to phosphate limited cell growth. With increasing phosphate limitation, a reduced cellular efficiency of ATP formation via respiratory chain activity and the ATP synthase complex was found for both strains. Process balancing, transcriptome analysis and flux balance analysis are pointing toward a multi-stage decoupling scenario, which in essence deteriorates the stoichiometric ratio of ATP formation to proton translocation, thereby affecting ATP availability from respiration and carbon usage. Starting off with a potential influence on ATP-synthase efficiency (stage 1), decoupling is further increased by modified respiratory activity (stage 2) and byproduct overflow (stage 3) finally resulting in a metabolic breakdown entering complete phosphate depletion (stage 4). The decoupling is initiated by phosphate limitation; further effects are mainly mediated on metabolic level through ATP availability and energy charge, additionally affected by ATP demanding product synthesis.
Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany. Electronic address: schuhmacher@ibvt.uni-stuttgart.de.
Tom
T
Schuhmacher
Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany. Electronic address: Michael.loeffler@ibvt.uni-stuttgart.de.
Michael
M
Löffler
Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany. Electronic address: thilo.hurler@arcor.de.
Thilo
T
Hurler
Institute of Biochemical Engineering, University of Stuttgart, Allmandring 31, D-70569 Stuttgart, Germany. Electronic address: takors@ibvt.uni-stuttgart.de.
Ralf
R
Takors
D000255:Adenosine Triphosphate / Q000378:metabolism; D002244:Carbon / Q000378:metabolism*; D004734:Energy Metabolism; D004926:Escherichia coli / Q000235:genetics / Q000254:growth & development* / Q000378:metabolism*; D005285:Fermentation; D020869:Gene Expression Profiling; D010710:Phosphates / Q000008:administration & dosage*; D014364:Tryptophan / Q000096:biosynthesis
D010710:Phosphates; D002244:Carbon; D014364:Tryptophan; D000255:Adenosine Triphosphate
Energy metabolism; Escherichia coli; Flux balance analysis; Phosphate starvation; Transcriptome analysis