SUITABILITY OF A DETERGENT-SENSITIVE ELECTRODE FOR THE DETERMINATION OF THE ABSORPTION OF CATIONIC DETERGENTS BY FUNGAL CONIDIAL CELLS

The study of the process of absorption of detergents by microbial cell s is important for the understanding of the mode-of-action of these ch emical agents in microorganisms. With the aim to study the absorption of alkyltrimethylammonium bromides by conidia of the phytopathogenic f ungus Botrytis cinerea, simple detergent-sensitive electrodes were con structed and tested for this purpose. The electrodes had a hexadecyltr imethyl-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 compa rison. The performance of the two types of electrodes was identical. T he response was linear between 10 and 100 mu M and the critical micell e concentration of the detergent, with slopes of ca. 45, 48 and 56 mV/ decade of activity, respectively, for dodecyl-, tetradecyl- and hexade cyl-trimethylammonium bromide. Direct comparison of potentiometry with the constructed detergent-sensitive electrodes, with a spectrophotome tric procedure based on the Orange G dye, indicated that these electro des are suitable to study the process of absorption of alkyltrimethyla mmonium bromides by B. cinerea conidia. The affinity of these molecule s to the spores increased with the length of the hydrocarbon chain of the detergent, and was reduced in the presence of Mg2+ or Ca2+, or at low pH, indicating that, as reported in the literature for the binding of cationic detergents to organic molecules, the absorption of the al kyltrimethylammonium bromides by B. cinerea spores was hydrophobic and ionic in nature.