Pseudomonas syringae is a phytopathogenic bacterium that causes lesions in leaves during the colonisation process. The damage is associated with production of many virulence factors, such as biofilm and phytotoxins. The essential oils of Thymus vulgaris (thyme) and Origanum vulgare (oregano) have been demonstrated to inhibit P. syringae. The aim of this study was to investigate the effects of T. vulgaris and O. vulgare essential oils on production of virulence factors of phytopathogenic P. syringae strains, including anti-biofilm and anti-toxins activities. The broth microdilution method was used for determination of MIC and biofilm inhibition assays. Coronatine, syringomycin and tabtoxin were pheno- and genotypically evaluated. Both oils showed good inhibitory activity against P. syringae, with MIC values from 1.43 to 11.5 mg·ml for thyme and 5.8 to 11.6 mg·ml for oregano. Biofilm formation, production of coronatine, syringomycin and tabtoxin were inhibited by thyme and oregano essential oil in most strains. The results presented here are promising, demonstrating the bactericidal activity and reduction of virulence factor production after treatment with thyme and oregano oil, providing insight into how they exert their antibacterial activity. These natural products could be considered in the future for the control of diseases caused by P. syringae.
As a follow-up to previous studies, the effects of Thymus vulgaris essential oil on selected virulence factors (growth, sessile cell survival, swimming, swarming, and exopolysaccharide production) were evaluated in phytopathogenic Pseudomonas syringae strains isolated from soybean fields in Argentina; reference strains Pseudomonas savastanoi pv. glycinea B076 and Pseudomonas aeruginosa PAO1. P. syringae are responsible for bacterial blight, a disease that affects crops worldwide. Plant bacterioses are usually treated with antibiotics and copper compounds, which may contribute to the development of resistance in pathogens and damage the environment. For these reasons, eco-friendly alternatives are necessary. Although aromatic plants are a natural source of antimicrobial substances, the effects of these substances on phytopathogenic bacteria remain largely unexplored. Subinhibitory concentrations of the oil significantly reduced the slope and rate of bacterial growth. In addition, biofilm and exopolysaccharide (EPS) production were inhibited, with swimming and swarming motility patterns being affected at all of the oil concentrations tested. Therefore, TEO could potentially be a highly efficient antipseudomonal agent for treating plant infections caused by P. syringae.
Phytopathogenic bacteria not only affect crop yield and quality but also the environment. Understanding the mechanisms involved in their survival is essential to develop new strategies to control plant disease. One such mechanism is the formation of biofilms; i.e., microbial communities within a three-dimensional structure that offers adaptive advantages, such as protection against unfavorable environmental conditions. Biofilm-producing phytopathogenic bacteria are difficult to manage. They colonize the intercellular spaces and the vascular system of the host plants and cause a wide range of symptoms such as necrosis, wilting, leaf spots, blight, soft rot, and hyperplasia. This review summarizes up-to-date information about saline and drought stress in plants (abiotic stress) and then goes on to focus on the biotic stress produced by biofilm-forming phytopathogenic bacteria, which are responsible for serious disease in many crops. Their characteristics, pathogenesis, virulence factors, systems of cellular communication, and the molecules implicated in the regulation of these processes are all covered.
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