The maintenance energy of bacteria in growing cultures

Pirt, S. J.

doi:10.1098/rspb.1965.0069

Cited by 1,190 publications

(252 citation statements)

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“…Its evaluation is obtained by adding to the base ATP yield of 41.25 mmol ATP/g-biomass for growth the total maintenance fluxes over all modes divided by the total growth rate from all the growth modes. 4,29 Y ATP=B ¼ overall ATP consumption rate by growthðr 23 Þand maintenanceðr 22 Þ biomass formation rate…”

Section: More Detailed Networkmentioning

confidence: 99%

A hybrid model of anaerobic E. coli GJT001: Combination of elementary flux modes and cybernetic variables

Kim

Varner

Ramkrishna

2008

Biotechnology Progress

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Flux balance analysis (FBA) in combination with the decomposition of metabolic networks into elementary modes has provided a route to modeling cellular metabolism. It is dependent, however, on the availability of external fluxes such as substrate uptake or growth rate before estimates can become available of intracellular fluxes. The framework classically does not allow modeling of metabolic regulation or the formulation of dynamic models except through dynamic measurement of external fluxes. The cybernetic modeling approach of Ramkrishna and coworkers provides a dynamic framework for modeling metabolic systems because of its focus on describing regulatory processes based on cybernetic arguments and hence has the capacity to describe both external and internal fluxes. In this article, we explore the alternative of developing hybrid models combining cybernetic models for the external fluxes with the flux balance approach for estimation of the internal fluxes. The approach has the merit of the simplicity of the early cybernetic models and hence computationally facile while also providing detailed information on intracellular fluxes. The hybrid model of this article is based on elementary mode decomposition of the metabolic network. The uptake rates for the various elementary modes are combined using global cybernetic variables based on maximizing substrate uptake rates. Estimation of intracellular metabolism is based on its stoichiometric coupling with the external fluxes under the assumption of (pseudo-) steady state conditions. The set of parameters of the hybrid model was estimated with the aid of nonlinear optimization routine, by fitting simulations with dynamic experimental data on concentrations of biomass, substrate, and fermentation products. The hybrid model estimations were tested with FBA (based on measured substrate uptake rate) for two different metabolic networks (one is a reduced network which fixes ATP contribution to the biomass and maintenance requirement of ATP, and the other network is a more complex network which has a separate reaction for maintenance.) for the same experiment involving anaerobic growth of E. coli GJT001. The hybrid model estimated glucose consumption and all fermentation byproducts to better than 10%. The FBA makes similar estimations of fermentation products, however, with the exception of succinate. The simulation results show that the global cybernetic variables alone can regulate the metabolic reactions obtaining a very satisfactory fit to the measured fermentation byproducts. In view of the hybrid model's ability to predict biomass growth and fermentation byproducts of anaerobic E. coli GJT001, this reduced order model offers a computationally efficient alternative to more detailed models of metabolism and hence useful for the simulation of bioreactors.

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Section: More Detailed Networkmentioning

confidence: 99%

A hybrid model of anaerobic E. coli GJT001: Combination of elementary flux modes and cybernetic variables

Kim

Varner

Ramkrishna

2008

Biotechnology Progress

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“…If the maintenance energy (Pirt 1965) is known, the experimental Y~,~, can be calculated according to:…”

Section: Atp Requirement For Anaerobic Chemostat Growth Of S Cerevismentioning

confidence: 99%

A theoretical evaluation of growth yields of yeasts

Verduyn

Stouthamer

Scheffers

et al. 1991

Antonie van Leeuwenhoek

214

176

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Growth yields of Saccharomyces cerevisiae and Candida utilis in carbon-limited chemostat cultures were evaluated. The yields on ethanol and acetate were much lower in S. cerevisiae, in line with earlier reports that site I phosphorylation is absent in this yeast. However, during aerobic growth on glucose both organisms had the same cell yield. This can be attributed to two factors: -S. cerevisiae had a lower protein content than C. utilis; -uptake of glucose by C. utilis requires energy whereas in S. cerevisiae it occurs via facilitated diffusion. Theoretical calculations showed that, as a result of these two factors, the ATP requirement for biomass formation in C. utilis is 35% higher than in S. cerevisiae (theoretical YATP values of 20.8 and 28.1, respectively). The experimental YATP for anaerobic growth of S. cerevisiae on glucose was 16 g biomass-mol ATP -1.In vivo P/O-ratios can be calculated for aerobic growth on ethanol and acetate, provided that the gap between the theoretical and experimental ATP requirements as observed for growth on glucose is taken into account. This was done in two ways: -via the assumption that the gap is independent of the growth substrate (i.e. a fixed amount of ATP bridges the difference between the theoretical and experimental values). -alternatively, on the assumption that the difference is a fraction of the total ATP expenditure, that is dependent on the substrate. Calculations of P/O-ratios for growth of both yeasts on glucose, ethanol, and acetate made clear that only by assuming a fixed difference between theoretical and experimental ATP requirements, the P/O-ratios are more or less independent of the growth substrate. These P/O-ratios are approximately 30% lower than the calculated mechanistic values.

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“…Moss et al [17] showed that when the glucose concentration for cell mass does not always remain constant. Pirt [22] suggested that the change in the "observed" cell mass yield coefficient was due to an energy of maintenance, described as the energy or substrate consumed for functions other than t.he production of new cell material ie. growth., Such functions may be the maintenance of solute gradients, turnover of macromolecules and motion.…”

Section: Navarro and Durandmentioning

confidence: 99%