title: Membrane hyperpolarisation by valinomycin and its limitations for bacterial viability assessment using rhodamine 123 and flow cytometry.
abstract: The ionophore, valinomycin, was investigated as a possible means of bacterial viability assessment using the fluorescent membrane potential dye rhodamine 123. Membrane hyperpolarisation in Escherichia coli, Pseudomonas fluorescens, Enterobacter aerogenes and Arthrobacter globiformis was examined during exponential growth and during stress by brief starvation in a high sodium, low potassium buffer using flow cytometric analysis of rhodamine 123 uptake. Dye uptake was variable both between species and amongst cells from the same culture. Exponential phase cells showed no increase in dye uptake due to valinomycin treatment. Stressed P. fluorescens cells responded to valinomycin treatment by increased dye uptake, while stressed E. coli and A. globiformis cells showed no response. Approximately 50% of stressed Eb. aerogenes cells responded to valinomycin. The results demonstrate the limitations of rhodamine dye for viability analysing the viability of diverse bacterial communities and underline the degree of cell heterogeneity in batch cultures.
authors.affiliation: Department of Genetics and Microbiology, University of Liverpool, UK.
authors.forename: J
authors.initials: J
authors.lastname: Porter
authors.forename: R
authors.initials: R
authors.lastname: Pickup
authors.forename: C
authors.initials: C
authors.lastname: Edwards
mesh_terms: D001173:Arthrobacter / Q000187:drug effects; D001419:Bacteria / Q000187:drug effects*; D001431:Bacteriological Techniques; D001692:Biological Transport; D002463:Cell Membrane Permeability / Q000187:drug effects*; D005434:Flow Cytometry; D005456:Fluorescent Dyes / Q000378:metabolism; D006090:Gram-Negative Bacteria / Q000187:drug effects; D007476:Ionophores / Q000494:pharmacology*; D020112:Rhodamine 123; D012235:Rhodamines / Q000378:metabolism; D014634:Valinomycin / Q000494:pharmacology*
chemical_list: D005456:Fluorescent Dyes; D007476:Ionophores; D012235:Rhodamines; D020112:Rhodamine 123; D014634:Valinomycin