Characterisation and action mode of Gluconacin, a bacteriocin with antimicrobial activity against Xanthomonas albilineans

Gluconacin, a bacteriocin produced by Gluconacetobacter diazotrophicus PAL5, has previously shown a large spectrum of inhibitory activity against beneficial and phytopathogenic bacteria. The present study proposes a three-dimensional (3D) structure for Gluconacin based on modelling and describes some physicochemical characteristics and the effect of the peptide on cells of the phytopathogenic bacterium Xanthomonas albilineans ICMP196. The Gluconacin 3D structural model results demonstrated the 7 alpha-helices and 11 beta-sheets. Growth inhibition of the indicator microorganism, X. albilineans, occurred in the first moments of contact with Gluconacin (0.25 mu g mu l(-1)). Treatment of bacterial cells caused significant loss of inorganic phosphate and UV-absorbing materials. Scanning electron microscopy images showed that Gluconacin-treated X. albilineans cells were fully lysed. These results suggest that the mode of action of this peptide involves altered membrane integrity and increased permeability, resulting in complete cell lysis. Physicochemical characterisation demonstrated stability of biological activity under high temperatures, including autoclaving conditions and low pH. The activity was reduced after treatment with proteases and some surfactants and abolished with ethylenediaminetetraacetic acid (EDTA). The 3D conformation model indicates the possibility of a hydrophobic region, which could possibly interact directly with the cell membrane of target bacteria. In conclusion, the ability of Gluconacin to inhibit growth of phytopathogens of agricultural importance opens up new opportunities for biotechnological applications and, consequently, a reduction in the use of pesticides.