Open AccessFluorescence measurements of free [Mg 2+ ] by use of mag‐fura 2 in Salmonella enterica
Author(s) -
Froschauer Elisabeth M,
Kolisek Martin,
Dieterich Frank,
Schweigel Monika,
Schweyen Rudolf J
Publication year - 2004
Publication title -
fems microbiology letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.899
H-Index - 151
eISSN - 1574-6968
pISSN - 0378-1097
DOI - 10.1111/j.1574-6968.2004.tb09677.x
Subject(s) - nigericin , valinomycin , biophysics , fluorescence , membrane potential , ionophore , salmonella enterica , membrane transport , chemistry , membrane , ion transporter , biochemistry , analytical chemistry (journal) , biology , escherichia coli , chromatography , quantum mechanics , physics , gene
The Mg 2+ fluorescent dye mag‐fura 2, entrapped in cells or organelles, has frequently been used for dual excitation ratio‐metric determinations of free ionic Mg 2+ concentrations in eukaryotic, mostly mammalian cells. Here we report its successful application to measure free Mg 2+ concentrations ([Mg 2+ ] i ) in Salmonella enterica cells. When kept in nominally Mg 2+ free buffer (resting conditions), the [Mg 2+ ] i of wild‐type cells has been determined to be 0.9 mM. An increase in the external Mg 2+ concentration ([Mg 2+ ] e ) resulted in a rapid increase of [Mg 2+ ] i , saturating within a few seconds at about 1.5 mM with [Mg 2+ ] e of 20 mM. In contrast, cells lacking the Mg 2+ transport proteins CorA, MgtA, MgtB failed to show this rapid increase. Instead, their [Mg 2+ ] i increased steadily over extended periods of time and saturated at concentrations below those of wild‐type cells. Mg 2+ uptake rates increased more than 15‐fold when corA was overexpressed in these mutant cells. Uptake of Mg 2+ into corA expressing cells was strongly stimulated by nigericin, which increased the membrane potential Δ Ψ at the expense of ΔpH, and drastically reduced by valinomycin, which decreased the membrane potential Δ Ψ . These results reveal mag‐fura 2 as a useful indicator to measure steady‐state [Mg 2+ ] i values in resting bacterial cells and to determine Mg 2+ uptake rates. They confirm the role of CorA as the major Mg 2+ transport protein and reveal the membrane potential as driving force for Mg 2+ uptake into S. enterica cells.