Suitability of a detergent-sensitive electrode for the determination of the absorption of cationic detergents by fungal conidial cells

Abstract

The study of the process of absorption of detergents by microbial cells is important for the understanding of the mode-of-action of these chemical agents in microorganisms. With the aim to study the absorption of alkyltrimethylammonium bromides by conidia of the phytopathogenic fungus Botrytis cinerea; simple detergent-sensitive electrodes were constructed and tested for this purpose. The electrodes had a hexadecyltrimethyl-ammonium bromide and tricresyl phosphate sensor system in poly-(vinylchloride) membranes. Electrodes with an internal reference, or with the membrane applied to a support made of electrically conductive silver-epoxy resin, were prepared and evaluated in parallel for comparison. The performance of the two types of electrodes was identical. The response was linear between 10 and 100 μM and the critical micelle concentration of the detergent, with slopes of ca. 45, 48 and 56 mV/decade of activity, respectively, for dodecyl-, tetradecyl- and hexadecyl-trimethylammonium bromide. Direct comparison of potentiometry with the constructed detergent-sensitive electrodes, with a spectrophotometric procedure based on the Orange G dye, indicated that these electrodes are suitable to study the process of absorption of alkyltrimethylammonium bromides by B. cinerea conidia. The affinity of these molecules to the spores increased with the length of the hydrocarbon chain of the detergent, and was reduced in the presence of Mg 2+ or Ca 2+, or at low pH, indicating that, as reported in the literature for the binding of cationic detergents to organic molecules, the absorption of the alkytrimethylammonium bromides by B. cinerea spores was hydrophobic and ionic in nature.