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      Bacterial fluoride resistance, Fluc channels, and the weak acid accumulation effect

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          Abstract

          Fluc channels protect bacteria from accumulating F in acidic environments.

          Abstract

          Fluoride ion (F ) is a ubiquitous environmental threat to microorganisms, which have evolved a family of highly selective “Fluc” F channels that export this inhibitory anion from their cytoplasm. It is unclear, however, how a thermodynamically passive mechanism like an ion channel can protect against high concentrations of external F . We monitored external F concentrations in Escherichia coli suspensions and showed that, in bacteria lacking Fluc, F accumulates when the external medium is acidified, as a predicted function of the transmembrane pH gradient. This weak acid accumulation effect, which results from the high pKa (3.4) and membrane permeability of HF, is abolished by Fluc channels. We also found that, although bacterial growth is inhibited by high concentrations of F , bacteria can withstand cytoplasmic F at levels a hundred times higher than those that inhibit proliferation, resuming growth when the F challenge is removed.

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          Condition-Dependent Cell Volume and Concentration of Escherichia coli to Facilitate Data Conversion for Systems Biology Modeling

          Systems biology modeling typically requires quantitative experimental data such as intracellular concentrations or copy numbers per cell. In order to convert population-averaging omics measurement data to intracellular concentrations or cellular copy numbers, the total cell volume and number of cells in a sample need to be known. Unfortunately, even for the often studied model bacterium Escherichia coli this information is hardly available and furthermore, certain measures (e.g. cell volume) are also dependent on the growth condition. In this work, we have determined these basic data for E. coli cells when grown in 22 different conditions so that respective data conversions can be done correctly. First, we determine growth-rate dependent cell volumes. Second, we show that in a 1 ml E. coli sample at an optical density (600 nm) of 1 the total cell volume is around 3.6 µl for all conditions tested. Third, we demonstrate that the cell number in a sample can be determined on the basis of the sample's optical density and the cells' growth rate. The data presented will allow for conversion of E. coli measurement data normalized to optical density into volumetric cellular concentrations and copy numbers per cell - two important parameters for systems biology model development.
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            pH homeostasis in Escherichia coli: measurement by 31P nuclear magnetic resonance of methylphosphonate and phosphate.

            The intracellular pH of Escherichia coli cells, respiring on endogenous energy sources, was monitored continuously by 31P NMR over an extracellular pH range between 5.5 and 9. pH homeostasis was found to be good over the entire range, with the data conforming to the simple relationship intracellular pH = 7.6 + 0.1(external pH - 7.6) so that the extreme values observed for intracellular pH were 7.4 and 7.8 at external pH 5.5 and 9, respectively. As well as inorganic phosphate, we employed the pH-sensitive NMR probe methylphosphonate, which was taken up by glycerol-grown cells and was nontoxic; its pKa of 7.65 made it an ideal probe for measurement of cytoplasmic pH and alkaline external pH.
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              Fluoride and organic weak acids as modulators of microbial physiology

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                Author and article information

                Journal
                J Gen Physiol
                J. Gen. Physiol
                jgp
                jgp
                The Journal of General Physiology
                The Rockefeller University Press
                0022-1295
                1540-7748
                September 2014
                : 144
                : 3
                : 257-261
                Affiliations
                [1 ]Department of Biochemistry and [2 ]Howard Hughes Medical Institute, Brandeis University, Waltham, MA 02453
                Author notes
                Correspondence to Christopher Miller: cmiller@ 123456brandeis.edu
                Article
                201411243
                10.1085/jgp.201411243
                4144673
                25156118
                4c05f2a5-3758-4a27-ba91-20abe0bf189c
                © 2014 Ji et al.

                This article is distributed under the terms of an Attribution–Noncommercial–Share Alike–No Mirror Sites license for the first six months after the publication date (see http://www.rupress.org/terms). After six months it is available under a Creative Commons License (Attribution–Noncommercial–Share Alike 3.0 Unported license, as described at http://creativecommons.org/licenses/by-nc-sa/3.0/).

                History
                : 11 June 2014
                : 23 July 2014
                Categories
                Research Articles

                Anatomy & Physiology
                Anatomy & Physiology

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