Abstract
One fundamental shortcoming of biotechnological processes operating
under carbon-limiting conditions is the high-energy demand (maintenance)
of the cells. Although the function of the central carbon metabolism in
supplying precursors and energy for biosynthesis has been thoroughly
characterized, its regulation and dynamic behaviour during
carbon-limited growth has not yet been revealed. The current work
demonstrates a time series of metabolic flux distributions during
fed-batch cultivation of Escherichia coli K-12 W3110 applying a constant
feed rate. The fluxes in glycolysis, pentose phosphate pathway and
biosynthesis fell significantly, whereas TCA cycle fluxes remained
constant. The flux redistribution resulted in an enhanced energy
generation in the TCA cycle and consequently, in a 20\% lower biomass
yield. The intracellular alarmones ppGpp and cAMP accumulated in large
quantities after the onset of nutrient limitation, subsequently
declining to basal levels. The network topology of the regulation of the
central metabolic pathways was identified so that the observed metabolic
and regulatory behaviour can be described. This provides novel aspects
of global regulation of the metabolism by the cra, crp and relA/spoT
modulons. The work constitutes an important step towards dynamic
mathematical modelling of regulation and metabolism, which is needed for
the rational optimization of biotechnological processes. (c) 2007
Elsevier B.V. All rights reserved.
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