Effects of plant antimicrobial phenolic compounds on virulence of the genus Pectobacterium

Janak Raj Joshi, Saul Burdman, Alexander Lipsky, Iris Yedidia

Department of Plant Pathology and Microbiology and the Otto Warburg Minerva Center for Agricultural Biotechnology, The Robert H. Smith Faculty of Agriculture, Food and Environment, The Hebrew University of Jerusalem, Rehovot, Israel.

Abstract

Pectobacterium spp. are among the most devastating necrotrophs, attacking more than 50% of angiosperm plant orders. Their virulence strategy is based mainly on the secretion of exoenzymes that degrade the cell walls of their hosts, providing nutrients to the bacteria, but conversely, exposing the bacteria to plant defense compounds. In the present study, we screened plant-derived antimicrobial compounds, mainly phenolic acids and polyphenols, for their ability to affect virulence determinants including motility, biofilm formation and extracellular enzyme activities of different Pectobacteria: Pectobacterium carotovorum, P. brasiliensis, P. atrosepticum and P. aroidearum. In addition, virulence assays were performed on three different plant hosts following exposure of the bacteria to selected phenolic compounds. These experiments showed that cinnamic, coumaric, syringic and salicylic acids and catechol can considerably reduce disease severity, ranging from 20 to 100%. The reduced disease severity was not only the result of reduced bacterial growth, but also of a direct effect of the compounds on important bacterial virulence determinants, including pectolytic and proteolytic exoenzyme activities, that were reduced by 50–100%. This is the first report revealing a direct effect of phenolic compounds on virulence factors in a wide range of Pectobacterium strains.

Keywords: Biofilm; Motility; Pectobacterium; Phenolics; Plant cell wall degrading enzymes; Virulence determinants.