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O2 as the regulatory signal for FNR-dependent gene regulation in Escherichia coli
S Becker1, G Holighaus, T Gabrielczyk
1Institut für Mikrobiologie und Weinforschung, Johannes Gutenberg-Universität Mainz, Germany.
Abstract:
With an oxystat, changes in the pattern of expression of FNR-dependent genes from Escherichia coli were studied as a function of the O2 tension (pO2) in the medium. Expression of all four tested genes was decreased by increasing O2. However, the pO2 values that gave rise to half-maximal repression (pO(0.5)) were dependent on the particular promoter and varied between 1 and 5 millibars (1 bar = 10(5) Pa). The pO(0.5) value for the ArcA-regulated succinate dehydrogenase genes was in the same range (pO(0.5) = 4.6 millibars). At these pO2 values, the cytoplasm can be calculated to be well supplied with O2 by diffusion. Therefore, intracellular O2 could provide the signal to FNR, suggesting that there is no need for a signal transfer chain. Genetic inactivation of the enzymes and coenzymes of aerobic respiration had no or limited effects on the pO(0.5) of FNR-regulated genes. Thus, neither the components of aerobic respiration nor their redox state are the primary sites for O2 sensing, supporting the significance of intracellular O2. Non-redox-active, structural O2 analogs like CO, CN-, and N3-, could not mimic the effect of O2 on FNR-regulated genes under anaerobic conditions and did not decrease the inhibitory effect of O2 under aerobic conditions.
Insights
Oxygen levels regulate gene expression in Escherichia coli. Intracellular oxygen, not respiration components, appears to be the primary signal for FNR-dependent genes, indicating no need for a complex signal transfer chain.
Area of Science:
- Microbiology
- Molecular Biology
- Biochemistry
Background:
- Gene expression in Escherichia coli is influenced by oxygen availability.
- The FNR protein (fumarate and nitrate reduction regulator) is a key transcriptional regulator responding to oxygen levels.
Purpose of the Study:
- To investigate how oxygen tension (pO2) affects the expression of FNR-dependent genes in Escherichia coli.
- To determine the site of oxygen sensing for FNR-regulated gene expression.
Main Methods:
- Utilized an oxystat to control and measure precise oxygen tensions in the growth medium.
- Studied the expression patterns of four FNR-dependent genes under varying pO2 conditions.
- Examined the effect of genetically inactivating aerobic respiration components on gene expression.
Main Results:
- Increasing oxygen levels led to decreased expression of all tested FNR-dependent genes.
- Half-maximal repression (pO(0.5)) varied between 1 and 5 millibars, specific to each promoter.
- Intracellular oxygen diffusion likely signals FNR, as respiration components did not significantly alter pO(0.5).
- Oxygen analogs (CO, CN-, N3-) did not mimic or alter oxygen's effect on gene expression.
Conclusions:
- Intracellular oxygen concentration is the primary signal for FNR-mediated gene regulation in Escherichia coli.
- Oxygen sensing for FNR-dependent genes does not rely on the redox state or components of aerobic respiration.
- A simple intracellular oxygen diffusion model adequately explains the observed regulatory patterns.