Caracterização da atividade antibacteriana do peptídeo Epsilon-Poli-L-Lisina contra Fitopatógenos

Abstract

Phytobacteria constitute an important group of plant pathogens, not only because of their high incidence in crops of economic value, but also because they are easily disseminated and are the cause of diseases that are difficult to control. Therefore, there is an urgent need to develop new control agents. Antimicrobial peptides (AMPs) are part of host defense in several organisms, and are considered potential therapeutic agents able to combat various pathogens due to their anti-viral, antifungal and antibacterial properties. An example of AMPs is the ɛ-Poly-L-lysine (ɛ-PL), a homopolypeptide formed by lysine residues, which demonstrated antimicrobial activity against several microorganisms, and presents some advantages such as water solubility, biodegradability, and non-toxicity, being a candidate for the control of phytopathogens. The aim of this study was to evaluate the antimicrobial activity of the ɛ-PL peptide against the phytobacteria Xanthomonas citri, Xanthomonas euvesicatoria, Ralstonia solanacearum and Agrobacterium tumefaciens. Spotting assays were conducted to determine the minimum inhibitory concentration (MIC) of the peptide and from the MIC values, mortality curve assays evaluated the bactericidal efficiency of the peptide over time by counting viable cells. Fluorescence spectroscopy and fluorescence microscopy quantified and visually demonstrated the fluorescence emitted by viable or non-viable bacteria. In order to see structural changes caused in the treated cells, scanning electron microscopy was performed. MICs were 80 μg ml-1 for X.citri, 400 μg ml-1 for A. tumefaciens, and 600 μg ml-1 for R. solanacearum and X. euvesicatoria, and the bactericidal effect of ɛ-PL was confirmed by mortality curve assays. Tomato plants inoculated with X.euvesicatoria were sprayed with ɛ-PL solution, and the reduction in disease severity was confirmed. ɛ-PL represents a promising alternative for the in vivo control of bacterial diseases.