CONICET | Buscador de Institutos y Recursos Humanos

The continuing global spread of antibiotic-resistant bacterial pathogens requires the developmentof alternative therapeutic strategies and bacteriocins are envisioned as an alternative [1].Bacteriocins are peptides or proteins produced by bacteria that exhibit narrow or broader activityspectra. Pseudomonas fluorescens SF4c produces tailocins, a phage-tail-like bacteriocins withantimicrobial activity against Xanthomonas vesicatoria Xcv Bv5-4a, a phytopathogenic strainsresponsible of bacterial-spot disease in tomato. We demonstrated, that tailocins adhere to the cellenvelope of strain Xcv Bv5-4a and cause the cellular death [2]. Although it has been proposedthat the action mechanism involve the pore formation in the membrane, direct structural evidenceof the damage at the molecular level is missing. Here we report studies using a high resolutionmicroscopy (AFM) in combination with a spectroscopic technique (IR scattering Scanning Near-Field Optical Microscopy, IR s-SNOM) to obtain information of surface topography simultaneouslywith opto-vibrational information in the near field overcoming the Abbe´s diffraction limit of spatialresolution. Besides the morphological differences observed between individuals X. vesicatoriaXcv Bv5-4a cells untreated (control) and treated with tailocins of P. fluorescens SF4c; the principalcomponent analysis (PCA) computed on the set of all acquired spectra allows to differentiatebetween the treated and control cells. The region from 1800 to 900 cm-1 assigned mainly tovibratory modes related to membrane phospholipids, ν C=O of lipids (1755 cm-1) and νas P=O ofphosphate groups (1240 cm-1) are modified, and can be associated to alterations in the structureof the cell envelope of Xcv Bv5-4a cells when are treated with tailocins. The results demonstratethat IR s-SNOM facilities available at the LNLS enable to study the biochemical nature to singlebacterium level at a nanoscale, without any special sample preparation.