Piscidin, an antibacterial peptide isolated from the mast cells of striped bass, has potent antimicrobial activity against a broad spectrum of pathogens in vitro. We investigated the mechanism of action of this 22-residue cationic peptide by carrying out structural studies and electrophysiological experiments in lipid bilayers. Circular dichroism experiments showed that piscidin was unstructured in water but had a high alpha-helix content in dodecylphosphocholine (DPC) micelles. 1H NMR data in water and TFE confirmed these results and demonstrated that the segment of residues 8-17 adopted an alpha-helical structure in a micellar environment. This molecule has a marked amphipathic character, due to well-defined hydrophobic and hydrophilic sectors. This structure is similar to those determined for other cationic peptides involved in permeabilization of the bacterial membrane. Multichannel experiments with piscidin incorporated into azolectin planar bilayers gave reproducible I-V curves at various peptide concentrations and unambiguously showed that this peptide permeabilized the membrane. This pore forming activity was confirmed by single-channel experiments, with well-defined ion channels obtained at different voltages. The characteristics of the ion channels (voltage dependence, only one or two states of conductance) clearly suggest that piscidin is more likely to permeabilize the membrane by toroidal pore formation rather than via the "barrel-stave" mechanism.

During the past 2 decades, considerable progress has been made in the study of bird semiochemistry, and our goal was to review and evaluate this literature with particular emphasis on the volatile organic constituents. Indeed, since the importance of social chemosignaling in birds is becoming more and more apparent, the search for molecules involved in chemical communication is of critical interest. These molecules can be found in different sources that include uropygial gland secretions, feather-surface compounds, and molecules from feces and skin. Although many studies have examined the chemical substances secreted by birds, research on bird chemical communication is still at the start, so new strategies for collecting samples and development of new methods of analysis are urgently required. As a first step, we built a database that brings together potential semiochemicals, using a unique chemical nomenclature for comparing different bird species and also for referencing the different classes of substances that can be found in order to adapt future parameters of analysis. The most important patterns of the wax fraction of preen secretions are highlighted and organized in an ordered table. We also draw up a list of various combinations of sampling and analytical techniques, so that each method can be compared at a glance.