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Carbon catabolite repression correlates with the maintenance of near invariant molecular crowding in proliferating E. coli cells.

Zhou Y, Vazquez A, Wise A, Warita T, Warita K, Bar-Joseph Z, Oltvai ZN - BMC Syst Biol (2013)

Bottom Line: We also find that forced transient increase of intracellular crowding or transient perturbation of CCR delay cell growth, the latter leading to associated cell density-and volume alterations.CCR is activated at an increased bacterial cell growth rate when it is required for optimal cell growth while intracellular macromolecular density is maintained within a narrow physiological range.In addition to CCR, there are likely to be other regulatory mechanisms of cell metabolism that have evolved to ensure optimal cell growth in the context of the fundamental biophysical constraint imposed by intracellular molecular crowding.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology, University of Pittsburgh, School of Medicine, S701 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15213, USA. oltvai@pitt.edu.

ABSTRACT

Background: Carbon catabolite repression (CCR) is critical for optimal bacterial growth, and in bacterial (and yeast) cells it leads to their selective consumption of a single substrate from a complex environment. However, the root cause(s) for the development of this regulatory mechanism is unknown. Previously, a flux balance model (FBAwMC) of Escherichia coli metabolism that takes into account the crowded intracellular milieu of the bacterial cell correctly predicted selective glucose uptake in a medium containing five different carbon sources, suggesting that CCR may be an adaptive mechanism that ensures optimal bacterial metabolic network activity for growth.

Results: Here, we show that slowly growing E. coli cells do not display CCR in a mixed substrate culture and gradual activation of CCR correlates with an increasing rate of E. coli cell growth and proliferation. In contrast, CCR mutant cells do not achieve fast growth in mixed substrate culture, and display differences in their cell volume and density compared to wild-type cells. Analyses of transcriptome data from wt E. coli cells indicate the expected regulation of substrate uptake and metabolic pathway utilization upon growth rate change. We also find that forced transient increase of intracellular crowding or transient perturbation of CCR delay cell growth, the latter leading to associated cell density-and volume alterations.

Conclusions: CCR is activated at an increased bacterial cell growth rate when it is required for optimal cell growth while intracellular macromolecular density is maintained within a narrow physiological range. In addition to CCR, there are likely to be other regulatory mechanisms of cell metabolism that have evolved to ensure optimal cell growth in the context of the fundamental biophysical constraint imposed by intracellular molecular crowding.

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Maltose regulon responses to its inducers in different growth media. Response of the maltose regulon genes to induction with 200 μm maltotriose and 4 mM cAMP in (A) glucose-, (B) galactose-, (C) glycerol-, (D) lactate-, and (E) maltose-limited cultures, and (F) mixed substrate medium, as measured by the activity of promoter-GFP constructs.
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Figure 2: Maltose regulon responses to its inducers in different growth media. Response of the maltose regulon genes to induction with 200 μm maltotriose and 4 mM cAMP in (A) glucose-, (B) galactose-, (C) glycerol-, (D) lactate-, and (E) maltose-limited cultures, and (F) mixed substrate medium, as measured by the activity of promoter-GFP constructs.

Mentions: Selected maltose operon promoters, such as malE and malK, whose gene products are subunits of the maltose transporter, responded strongly to the inducers, maltotriose and cAMP, in glucose-, galactose-, and glycerol-limited cultures (Figure 2A-C) and displayed milder responses in lactate- and maltose-limited cultures (Figure 2D, E). In contrast, delayed and repressed promoter responses were evident in the mixed substrate culture (Figure 2F). Of note, the repressed gene activities in mixed substrate cannot be interpreted as higher basal gene activity because the GFP/OD levels in mixed substrate culture were similar to that in the maltose culture (data not shown). These data indicate the presence of stronger CCR in mixed substrate- than in single substrate-limited growth media.


Carbon catabolite repression correlates with the maintenance of near invariant molecular crowding in proliferating E. coli cells.

Zhou Y, Vazquez A, Wise A, Warita T, Warita K, Bar-Joseph Z, Oltvai ZN - BMC Syst Biol (2013)

Maltose regulon responses to its inducers in different growth media. Response of the maltose regulon genes to induction with 200 μm maltotriose and 4 mM cAMP in (A) glucose-, (B) galactose-, (C) glycerol-, (D) lactate-, and (E) maltose-limited cultures, and (F) mixed substrate medium, as measured by the activity of promoter-GFP constructs.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3924228&req=5

Figure 2: Maltose regulon responses to its inducers in different growth media. Response of the maltose regulon genes to induction with 200 μm maltotriose and 4 mM cAMP in (A) glucose-, (B) galactose-, (C) glycerol-, (D) lactate-, and (E) maltose-limited cultures, and (F) mixed substrate medium, as measured by the activity of promoter-GFP constructs.
Mentions: Selected maltose operon promoters, such as malE and malK, whose gene products are subunits of the maltose transporter, responded strongly to the inducers, maltotriose and cAMP, in glucose-, galactose-, and glycerol-limited cultures (Figure 2A-C) and displayed milder responses in lactate- and maltose-limited cultures (Figure 2D, E). In contrast, delayed and repressed promoter responses were evident in the mixed substrate culture (Figure 2F). Of note, the repressed gene activities in mixed substrate cannot be interpreted as higher basal gene activity because the GFP/OD levels in mixed substrate culture were similar to that in the maltose culture (data not shown). These data indicate the presence of stronger CCR in mixed substrate- than in single substrate-limited growth media.

Bottom Line: We also find that forced transient increase of intracellular crowding or transient perturbation of CCR delay cell growth, the latter leading to associated cell density-and volume alterations.CCR is activated at an increased bacterial cell growth rate when it is required for optimal cell growth while intracellular macromolecular density is maintained within a narrow physiological range.In addition to CCR, there are likely to be other regulatory mechanisms of cell metabolism that have evolved to ensure optimal cell growth in the context of the fundamental biophysical constraint imposed by intracellular molecular crowding.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pathology, University of Pittsburgh, School of Medicine, S701 Scaife Hall, 3550 Terrace Street, Pittsburgh, PA 15213, USA. oltvai@pitt.edu.

ABSTRACT

Background: Carbon catabolite repression (CCR) is critical for optimal bacterial growth, and in bacterial (and yeast) cells it leads to their selective consumption of a single substrate from a complex environment. However, the root cause(s) for the development of this regulatory mechanism is unknown. Previously, a flux balance model (FBAwMC) of Escherichia coli metabolism that takes into account the crowded intracellular milieu of the bacterial cell correctly predicted selective glucose uptake in a medium containing five different carbon sources, suggesting that CCR may be an adaptive mechanism that ensures optimal bacterial metabolic network activity for growth.

Results: Here, we show that slowly growing E. coli cells do not display CCR in a mixed substrate culture and gradual activation of CCR correlates with an increasing rate of E. coli cell growth and proliferation. In contrast, CCR mutant cells do not achieve fast growth in mixed substrate culture, and display differences in their cell volume and density compared to wild-type cells. Analyses of transcriptome data from wt E. coli cells indicate the expected regulation of substrate uptake and metabolic pathway utilization upon growth rate change. We also find that forced transient increase of intracellular crowding or transient perturbation of CCR delay cell growth, the latter leading to associated cell density-and volume alterations.

Conclusions: CCR is activated at an increased bacterial cell growth rate when it is required for optimal cell growth while intracellular macromolecular density is maintained within a narrow physiological range. In addition to CCR, there are likely to be other regulatory mechanisms of cell metabolism that have evolved to ensure optimal cell growth in the context of the fundamental biophysical constraint imposed by intracellular molecular crowding.

Show MeSH
Related in: MedlinePlus