Phosphonates of Pectobacterium atrosepticum: Discovery and Role in Plant–Pathogen Interactions

Many phytopathogens' gene products that contribute to plant-pathogen interactions remain unexplored. In one of the most harmful phytopathogenic bacterium <i>Pectobacterium atrosepticum</i> (<i>Pba</i>), phosphonate-related genes have been previously shown to be among the most upregulated following host plant colonization. However, phosphonates, compounds characterized by a carbon-phosphorus bond in their composition, have not been described in <i>Pectobacterium</i> species and other phytopathogenic bacteria, with the exception of <i>Pseudomonas syringae</i> and <i>Pantoea ananatis</i>. Our study aimed to determine whether <i>Pba</i> synthesizes extracellular phosphonates and, if so, to analyze their physiological functions. We demonstrated that <i>Pba</i> produces two types of extracellular phosphonates: 2-diethoxyphosphorylethanamine and phenylphosphonic acid. Notably, such structures have not been previously described among natural phosphonates. The production of <i>Pba</i> phosphonates was shown to be positively regulated by quorum sensing and in the presence of pectic compounds. <i>Pba</i> phosphonates were found to have a positive effect on <i>Pba</i> stress resistance and a negative effect on <i>Pba</i> virulence. The discovered <i>Pba</i> phosphonates are discussed as metabolites that enable <i>Pba</i> to control its "harmful properties", thereby maintaining its ecological niche (the host plant) in a relatively functional state for an extended period.