Thermodynamic Correlation for imax

The value imax is the result of a limiting factor in metabolism. This metabolism can be represented very schematically as shown in Figure 9. Three possible bottlenecks are identified (Fig. 9):

Substrate l

Biomass

Gibbs energy

Figure 9. Possible bottlenecks in metabolism.

3. The rate of making Gibbs energy available to enable growth and maintenance

Here we assume as a simple working hypothesis that the rate of making Gibbs energy available for microorganisms is limited by a maximum rate of electron transport in the catabolic energy production. This hypothesis is supported by studies with Escherichia coli, where imax was measured aerobically (at the same temperature) for different growth substrates (32). It was observed that for all substrates the same maximal biomass specific O2 uptake rate was achieved by E. coli. This supports the hypothesis of a constant maximal electron-transport capacity in microorganisms. A similar hypothesis was put forward by McCarthy (26). The following correlation is now proposed for the maximal electron-transport capacity in the micro-bial electron transport chain (in mol electrons/C-mol bio-mass/h) as a function of temperature:

Maximal electron-transport capacity

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