Basic Regulatory Principles of Escherichia coli's Electron Transport Chain for Varying Oxygen Conditions
For adaptation between anaerobic, micro-aerobic and aerobic conditions Escherichia coli's metabolism and in particular its electron transport chain (ETC) is highly regulated. Although it is known … that the global transcriptional regulators FNR and ArcA are involved in oxygen response it is unclear how they interplay in the regulation of ETC enzymes under micro-aerobic chemostat conditions. Also, there are diverse results which and how quinones (oxidised/reduced, ubiquinone/other quinones) are controlling the ArcBA two-component system. In the following a mathematical model of the E. coli ETC linked to basic modules for substrate uptake, fermentation product excretion and biomass formation is introduced. The kinetic modelling focusses on regulatory principles of the ETC for varying oxygen conditions in glucose-limited continuous cultures. The model is based on the balance of electron donation (glucose) and acceptance (oxygen or other acceptors). Also, it is able to account for different chemostat conditions due to changed substrate concentrations and dilution rates. The parameter identification process is divided into an estimation and a validation step based on previously published and new experimental data. The model shows that experimentally observed, qualitatively different behaviour of the ubiquinone redox state and the ArcA activity profile in the micro-aerobic range for different experimental conditions can emerge from a single network structure. The network structure features a strong feed-forward effect from the FNR regulatory system to the ArcBA regulatory system via a common control of the dehydrogenases of the ETC. The model supports the hypothesis that ubiquinone but not ubiquinol plays a key role in determining the activity of ArcBA in a glucose-limited chemostat at micro-aerobic conditions.
Date Published: 30th Sep 2014
Journal: PLoS One
The concentration of molecular oxygen (O(2)) began to increase in the Earth's atmosphere approximately two billion years ago. Its presence posed a threat to anaerobes but also offered opportunities … for improved energy conservation via aerobic respiration. The ability to sense environmental O(2) thus became, and remains, important for many bacteria, both for protection and switching between anaerobic and aerobic respiration. Utilizing an iron-sulfur cluster as the sensor of O(2) exploits the ability of O(2) to oxidize the iron-sulfur cluster, ultimately resulting in cluster disassembly. When utilizing heme as the sensor, the capacity of O(2) to form a reversible Fe-O(2) bond or alternatively the oxidation of the heme iron atom itself is used to detect O(2) and switch regulators between active and inactive forms.
Authors: Jeff Green, Jason C Crack, Andrew J Thomson, Nick E LeBrun
Date Published: 24th Feb 2009
Journal: Curr. Opin. Microbiol.