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5 Publications visible to you, out of a total of 5
On the function of the various quinone species in Escherichia coli

Abstract (Expand)

The respiratory chain of Escherichia coli contains three quinones. Menaquinone and demethylmenaquinone have low midpoint potentials and are involved in anaerobic respiration, while ubiquinone, which … has a high midpoint potential, is involved in aerobic and nitrate respiration. Here, we report that demethylmenaquinone plays a role not only in trimethylaminooxide-, dimethylsulfoxide- and fumarate-dependent respiration, but also in aerobic respiration. Furthermore, we demonstrate that demethylmenaquinone serves as an electron acceptor for oxidation of succinate to fumarate, and that all three quinol oxidases of E. coli accept electrons from this naphtoquinone derivative.

Authors: , , Klaas J. Hellingwerf,

Date Published: 1st Sep 2012

Publication Type: Not specified

Uncoupling of substrate-level phosphorylation in Escherichia coli during glucose-limited growth

Abstract (Expand)

The respiratory chain of Escherichia coli contains three different cytochrome oxidases. Whereas the cytochrome bo oxidase and the cytochrome bd-I oxidase are well characterized and have been shown to … contribute to proton translocation, physiological data suggested a nonelectrogenic functioning of the cytochrome bd-II oxidase. Recently, however, this view was challenged by an in vitro biochemical analysis that showed that the activity of cytochrome bd-II oxidase does contribute to proton translocation with an H(+)/e(-) stoichiometry of 1. Here, we propose that this apparent discrepancy is due to the activities of two alternative catabolic pathways: the pyruvate oxidase pathway for acetate production and a pathway with methylglyoxal as an intermediate for the production of lactate. The ATP yields of these pathways are lower than those of the pathways that have so far always been assumed to catalyze the main catabolic flux under energy-limited growth conditions (i.e., pyruvate dehydrogenase and lactate dehydrogenase). Inclusion of these alternative pathways in the flux analysis of growing E. coli strains for the calculation of the catabolic ATP synthesis rate indicates an electrogenic function of the cytochrome bd-II oxidase, compatible with an H(+)/e(-) ratio of 1. This analysis shows for the first time the extent of bypassing of substrate-level phosphorylation in E. coli under energy-limited growth conditions.

Authors: , Klaas J Hellingwerf, Maarten J Teixeira de Mattos,

Date Published: 27th Jul 2012

Publication Type: Not specified

Growth rate dependent control in Enterococcus faecalis: effects on the transcriptome, proteome and strong regulation of lactate dehydrogenase

Abstract (Expand)

Enterococcus faecalis V583 was grown in a glucose-limited chemostat at three different (0.05 h(-1), 0.15 h(-1) and 0.4 h(-1)) growth rates. The fermentation pattern changed with growth rate, from a … mostly homolactic profile at high growth rate to a fermentation dominated by formate, acetate and ethanol production at low growth rate. A number of amino acids were consumed at the lower growth rates but not by fast growing cells. The change in metabolic profile was mainly caused by decreased flux through lactate dehydrogenase. Transcription of ldh-1, encoding the principal lactate dehydrogenase, showed very strong growth rate dependence and differed by three orders of magnitude between the highest and the lowest growth rates. Despite the increase in ldh-1 transcript, the content of the Ldh-1 protein was the same under all conditions. Using microarrays and qPCR the levels of 227 gene transcript were found to be affected by the growth rate, and 56 differentially expressed proteins were found by proteomic analyses. Few genes or proteins showed a growth rate-dependent increase or decrease in expression over the whole range of conditions, and many showed at maximum or minimum at the middle growth rate (D=0.15h(-1)). For many gene products a discrepancy between transcriptomic and proteomic data were seen, indicating post-transcriptional regulation of expression.

Authors: , Ellen M Faergestad, , Lars Snipen, ,

Date Published: 1st Nov 2011

Publication Type: Not specified

Physiological characterization of three lactic acid bacteria and their isogenic ldh deletion mutants shows that these organisms are optimized for Yatp and not ATP formation rates at their physiological pH

Abstract (Expand)

Several lactic acid bacteria use homolactic fermentation for generation of ATP. Here we studied the role of the lactate dehydrogenase enzyme on the general physiology of the three homolactic acid … bacteria Lactococcus lactis, Enterococcus faecalis and Streptococcus pyogenes. Of note, deletion of the ldh genes hardly affected the growth rate in chemically defined medium in microaerophilic conditions. However, growth rate was affected in rich medium. Furthermore, deletion of ldh affected the ability for utilization of various substrates as a carbon source. A switch to mixed acid fermentation was observed in glucose-limited continuous growth and was dependent on the growth rate for S. pyogenes and dependent on the pH for E. faecalis. In S. pyogenes and L. lactis a change in pH resulted in a clear change in Yatp. The pH that showed the highest Yatp corresponded to the pH of the natural habitat of the organisms.

Authors: , , , , Anja Pritzschke, Nikolai Siemens, , ,

Date Published: 25th Nov 2010

Publication Type: Not specified

Construction and characterization of three lactate dehydrogenase-negative Enterococcus faecalis V583 mutants

Abstract (Expand)

The roles of the two ldh genes of Enterococcus faecalis were studied using knockout mutants. Deletion of ldh-1 causes a metabolic shift from homolactic fermentation to ethanol, formate, and acetoin … production, with a high level of formate production even under aerobic conditions. Ldh-2 plays only a minor role in lactate production.

Authors: , Zhian Saleihan, ,

Date Published: 22nd May 2009

Publication Type: Not specified

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