LIMITATIONS OF THE USE OF AN ION-SELECTIVE ELECTRODE IN THE STUDY OF THE UPTAKE OF CU2+ BY PSEUDOMONAS-SYRINGAE CELLS

During the passive uptake of Cu2+, added to cell suspensions of the phytopathogenic bacterium Pseudomonas syringae, the extracellular free Cu2+ concentration (assayed by ion-selective electrode potentiometry) was significantly lower than the extracellular total copper concentration (assayed by atomic absorption spectrophotometry), indicating that the uptake of Cu2+ by this bacterium could not be accurately followed using a Cu2+-selective electrode. The results from this and previous studies suggest that some of the metabolites (namely nucleotides, RNAs and inorganic phosphate) released from P. syringae cells bound a significant fraction of the Cu2+ added to the suspension. The results emphasize the limitations of the use of an ion-selective electrode to study the uptake of metals by bacterial cells, and the need to consider the extracellular composition of the suspensions when studying the interactions between metal ions and bacterial cells.