Publications

Abstract (Expand)

Escherichia coli is a facultatively anaerobic bacterium. With glucose if no external electron acceptors are available, ATP is produced by substrate level phosphorylation. The intracellular redox balance is maintained by mixed-acid fermentation, that is, the production and excretion of several organic acids. When oxygen is available, E. coli switches to aerobic respiration to achieve redox balance and optimal energy conservation by proton translocation linked to electron transfer. The switch between fermentative and aerobic respiratory growth is driven by extensive changes in gene expression and protein synthesis, resulting in global changes in metabolic fluxes and metabolite concentrations. This oxygen response is determined by the interaction of global and local genetic regulatory mechanisms, as well as by enzymatic regulation. The response is affected by basic physical constraints such as diffusion, thermodynamics and the requirement for a balance of carbon, electrons and energy (predominantly the proton motive force and the ATP pool). A comprehensive systems level understanding of the oxygen response of E. coli requires the integrated interpretation of experimental data that are pertinent to the multiple levels of organization that mediate the response. In the pan-European venture, Systems Biology of Microorganisms (SysMO) and specifically within the project Systems Understanding of Microbial Oxygen Metabolism (SUMO), regulator activities, gene expression, metabolite levels and metabolic flux datasets were obtained using a standardized and reproducible chemostat-based experimental system. These different types and qualities of data were integrated using mathematical models. The approach described here has revealed a much more detailed picture of the aerobic-anaerobic response, especially for the environmentally critical microaerobic range that is located between unlimited oxygen availability and anaerobiosis.

Authors: Katja Bettenbrock, Hao Bai, Michael Ederer, Jeff Green, Klaas Hellingwerf, Michael Holcombe, S. Kunz, Matthew Rolfe, Guido Sanguinetti, Oliver Sawodny, Poonam Sharma, Sonja Steinsiek, Robert Poole

Date Published: 7th May 2014

Journal: Adv Microb Physiol

Abstract (Expand)

Oxygen availability is the major determinant of the metabolic modes adopted by Escherichia coli. Whilst much is known about E. coli gene expression and metabolism under fully aerobic and anaerobic conditions, the intermediate oxygen tensions that are encountered in natural niches are understudied. Here for the first time the transcript profiles of E. coli K-12 across the physiologically significant range of oxygen availabilities are described. These suggested a progressive switch to aerobic respiratory metabolism and a remodeling of the cell envelope as oxygen availability increased. The transcriptional responses were consistent with changes in the abundances of cytochrome bd and bo and outer membrane protein W. The observed transcript and protein profiles result from changes in the activities of regulators that respond to oxygen itself, or to metabolic and environmental signals that are sensitive to oxygen availability (aerobiosis). A probabilistic model (TFinfer) was used to predict the activity of the indirect oxygen-sensing two-component system ArcBA across the aerobiosis range. The model implied that the activity of the regulator ArcA correlated with aerobiosis, but not with the redox state of the ubiquinone pool, challenging the idea that ArcA activity is inhibited by oxidized ubiquinone. Measurement of the amount of phosphorylated ArcA correlated with the predicted ArcA activities and with aerobiosis, suggesting that fermentation product-mediated inhibition of ArcB phosphatase activity is the dominant mechanism for regulating ArcA activity under the conditions used here.

Authors: Matthew Rolfe, Alexander Ter Beek, Alison Graham, Eleanor W Trotter, H M Shahzad Asif, Guido Sanguinetti, Joost Teixeira De Mattos, Robert Poole, Jeff Green

Date Published: 22nd Jan 2011

Journal: Not specified

Abstract (Expand)

SUMMARY: TFInfer is a novel open access, standalone tool for genome-wide inference of transcription factor activities from gene expression data. Based on an earlier MATLAB version, the software has now been extended in a number of ways. It has been significantly optimised in terms of performance, and it was given novel functionality, by allowing the user to model both time series and data from multiple independent conditions. With a full documentation and intuitive graphical user interface, together with an in-built data base of yeast and Escherichia coli transcription factors, the software does not require any mathematical or computational expertise to be used effectively. AVAILABILITY: http://homepages.inf.ed.ac.uk/gsanguin/TFInfer.html CONTACT: gsanguin@staffmail.ed.ac.uk SUPPLEMENTARY INFORMATION: Supplementary data are available at Bioinformatics online.

Authors: H M Shahzad Asif, Matthew Rolfe, Jeff Green, Neil D Lawrence, Magnus Rattray, Guido Sanguinetti

Date Published: 24th Aug 2010

Journal: Bioinformatics

Abstract (Expand)

Fumarate and nitrate reduction regulatory (FNR) proteins are bacterial transcription factors that coordinate the switch between aerobic and anaerobic metabolism. In the absence of O(2), FNR binds a [4Fe-4S](2+) cluster (ligated by Cys-20, 23, 29, 122) promoting the formation of a transcriptionally active dimer. In the presence of O(2), FNR is converted into a monomeric, non-DNA-binding form containing a [2Fe-2S](2+) cluster. The reaction of the [4Fe-4S](2+) cluster with O(2) has been shown to proceed via a 2-step process, an O(2)-dependent 1-electron oxidation to yield a [3Fe-4S](+) intermediate with release of 1 Fe(2+) ion, followed by spontaneous rearrangement to the [2Fe-2S](2+) form with release of 1 Fe(3+) and 2 S(2-) ions. Here, we show that replacement of Ser-24 by Arg, His, Phe, Trp, or Tyr enhances aerobic activity of FNR in vivo. The FNR-S24F protein incorporates a [4Fe-4S](2+) cluster with spectroscopic properties similar to those of FNR. However, the substitution enhances the stability of the [4Fe-4S](2+) cluster in the presence of O(2). Kinetic analysis shows that both steps 1 and 2 are slower for FNR-S24F than for FNR. A molecular model suggests that step 1 of the FNR-S24F iron-sulfur cluster reaction with O(2) is inhibited by shielding of the iron ligand Cys-23, suggesting that Cys-23 or the cluster iron bound to it is a primary site of O(2) interaction. These data lead to a simple model of the FNR switch with physiological implications for the ability of FNR proteins to operate over different ranges of in vivo O(2) concentrations.

Authors: Adrian J Jervis, Jason C Crack, Gaye White, Peter J Artymiuk, Myles R Cheesman, Andrew J Thomson, Nick E Le Brun, Jeff Green

Date Published: 4th Mar 2009

Journal: Proc. Natl. Acad. Sci. U.S.A.

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