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Extensive exometabolome analysis reveals extended overflow metabolism in various microorganisms.

Paczia N, Nilgen A, Lehmann T, Gätgens J, Wiechert W, Noack S - Microb. Cell Fact. (2012)

Bottom Line: Most surprisingly, in all cases a great diversity of central metabolic intermediates and amino acids is found in the culture medium with extracellular concentrations varying in the micromolar range.As a result, the intermediates in the culture medium during batch growth must originate from passive or active transportation due to a new phenomenon termed "extended" overflow metabolism.In turn, this finding has consequences for metabolite balancing and, particularly, for intracellular metabolite quantification and (13)C-metabolic flux analysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Bio- and Geosciences, Biotechnology, Systems Biotechnology, Forschungszentrum Jülich GmbH, Jülich, Germany.

ABSTRACT
Overflow metabolism is well known for yeast, bacteria and mammalian cells. It typically occurs under glucose excess conditions and is characterized by excretions of by-products such as ethanol, acetate or lactate. This phenomenon, also denoted the short-term Crabtree effect, has been extensively studied over the past few decades, however, its basic regulatory mechanism and functional role in metabolism is still unknown. Here we present a comprehensive quantitative and time-dependent analysis of the exometabolome of Escherichia coli, Corynebacterium glutamicum, Bacillus licheniformis, and Saccharomyces cerevisiae during well-controlled bioreactor cultivations. Most surprisingly, in all cases a great diversity of central metabolic intermediates and amino acids is found in the culture medium with extracellular concentrations varying in the micromolar range. Different hypotheses for these observations are formulated and experimentally tested. As a result, the intermediates in the culture medium during batch growth must originate from passive or active transportation due to a new phenomenon termed "extended" overflow metabolism. Moreover, we provide broad evidence that this could be a common feature of all microorganism species when cultivated under conditions of carbon excess and non-inhibited carbon uptake. In turn, this finding has consequences for metabolite balancing and, particularly, for intracellular metabolite quantification and (13)C-metabolic flux analysis.

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Exometabolome analysis of Escherichia coli and Bacillus licheniformis. (A) Batch cultivation of E. coli WT on defined media with 20 g l-1 glucose. (B) Batch cultivation of B. licheniformis WT on defined media with 16 g l-1 glucose. Abbreviations: OD, optical density; Glc, glucose; CO2, offgas carbon dioxide; pO2, dissolved oxygen; G6P, glucose-6-phosphate; PYR, pyruvate; ACT, acetate; HOM, homoserine; TYR, tyrosine; VAL, valine; F6P, fructose-6-phosphate; GLY, glycine; ASN, asparagine; LYS, lysine.
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Figure 1: Exometabolome analysis of Escherichia coli and Bacillus licheniformis. (A) Batch cultivation of E. coli WT on defined media with 20 g l-1 glucose. (B) Batch cultivation of B. licheniformis WT on defined media with 16 g l-1 glucose. Abbreviations: OD, optical density; Glc, glucose; CO2, offgas carbon dioxide; pO2, dissolved oxygen; G6P, glucose-6-phosphate; PYR, pyruvate; ACT, acetate; HOM, homoserine; TYR, tyrosine; VAL, valine; F6P, fructose-6-phosphate; GLY, glycine; ASN, asparagine; LYS, lysine.

Mentions: The growth of E. coli proceeded in a typical batch mode manner (Figure 1A). During the exponential phase the substrate glucose was converted to biomass and the main by-products carbon dioxide, pyruvate and acetate. Exponential growth stopped about 8 h after inoculation at a remaining glucose concentration of cGlc ≈ 6 g l-1. In the following transitory phase, glucose was further consumed and the cells also started to take up the preliminary by-products pyruvate and acetate in parallel. When the glucose was nearly exhausted a very short stationary phase was observed, until finally the biomass concentration slowly began to decrease and carbon dioxide formation rapidly dropped.


Extensive exometabolome analysis reveals extended overflow metabolism in various microorganisms.

Paczia N, Nilgen A, Lehmann T, Gätgens J, Wiechert W, Noack S - Microb. Cell Fact. (2012)

Exometabolome analysis of Escherichia coli and Bacillus licheniformis. (A) Batch cultivation of E. coli WT on defined media with 20 g l-1 glucose. (B) Batch cultivation of B. licheniformis WT on defined media with 16 g l-1 glucose. Abbreviations: OD, optical density; Glc, glucose; CO2, offgas carbon dioxide; pO2, dissolved oxygen; G6P, glucose-6-phosphate; PYR, pyruvate; ACT, acetate; HOM, homoserine; TYR, tyrosine; VAL, valine; F6P, fructose-6-phosphate; GLY, glycine; ASN, asparagine; LYS, lysine.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3526501&req=5

Figure 1: Exometabolome analysis of Escherichia coli and Bacillus licheniformis. (A) Batch cultivation of E. coli WT on defined media with 20 g l-1 glucose. (B) Batch cultivation of B. licheniformis WT on defined media with 16 g l-1 glucose. Abbreviations: OD, optical density; Glc, glucose; CO2, offgas carbon dioxide; pO2, dissolved oxygen; G6P, glucose-6-phosphate; PYR, pyruvate; ACT, acetate; HOM, homoserine; TYR, tyrosine; VAL, valine; F6P, fructose-6-phosphate; GLY, glycine; ASN, asparagine; LYS, lysine.
Mentions: The growth of E. coli proceeded in a typical batch mode manner (Figure 1A). During the exponential phase the substrate glucose was converted to biomass and the main by-products carbon dioxide, pyruvate and acetate. Exponential growth stopped about 8 h after inoculation at a remaining glucose concentration of cGlc ≈ 6 g l-1. In the following transitory phase, glucose was further consumed and the cells also started to take up the preliminary by-products pyruvate and acetate in parallel. When the glucose was nearly exhausted a very short stationary phase was observed, until finally the biomass concentration slowly began to decrease and carbon dioxide formation rapidly dropped.

Bottom Line: Most surprisingly, in all cases a great diversity of central metabolic intermediates and amino acids is found in the culture medium with extracellular concentrations varying in the micromolar range.As a result, the intermediates in the culture medium during batch growth must originate from passive or active transportation due to a new phenomenon termed "extended" overflow metabolism.In turn, this finding has consequences for metabolite balancing and, particularly, for intracellular metabolite quantification and (13)C-metabolic flux analysis.

View Article: PubMed Central - HTML - PubMed

Affiliation: Institute of Bio- and Geosciences, Biotechnology, Systems Biotechnology, Forschungszentrum Jülich GmbH, Jülich, Germany.

ABSTRACT
Overflow metabolism is well known for yeast, bacteria and mammalian cells. It typically occurs under glucose excess conditions and is characterized by excretions of by-products such as ethanol, acetate or lactate. This phenomenon, also denoted the short-term Crabtree effect, has been extensively studied over the past few decades, however, its basic regulatory mechanism and functional role in metabolism is still unknown. Here we present a comprehensive quantitative and time-dependent analysis of the exometabolome of Escherichia coli, Corynebacterium glutamicum, Bacillus licheniformis, and Saccharomyces cerevisiae during well-controlled bioreactor cultivations. Most surprisingly, in all cases a great diversity of central metabolic intermediates and amino acids is found in the culture medium with extracellular concentrations varying in the micromolar range. Different hypotheses for these observations are formulated and experimentally tested. As a result, the intermediates in the culture medium during batch growth must originate from passive or active transportation due to a new phenomenon termed "extended" overflow metabolism. Moreover, we provide broad evidence that this could be a common feature of all microorganism species when cultivated under conditions of carbon excess and non-inhibited carbon uptake. In turn, this finding has consequences for metabolite balancing and, particularly, for intracellular metabolite quantification and (13)C-metabolic flux analysis.

Show MeSH
Related in: MedlinePlus