Inhibition of Xanthomonas fragariae, Causative Agent of Angular Leaf Spot of Strawberry, through Iron Deprivation

Abstract

In commercial production settings, few options exist to prevent or treat angular leaf spot (ALS) of strawberry, a disease of economic importance and caused by the bacterial pathogen Xanthomonas fragariae. In the process of isolating and identifying X. fragariae bacteria from symptomatic plants, we observed growth inhibition of X. fragariae by bacterial isolates from the same leaf macerates. Identified as species of Pseudomonas and Rhizobium, these isolates were confirmed to suppress growth of X. fragariae in agar overlay plates and in microtiter plate cultures, as did our reference strain Pseudomonas putida KT2440. Screening of a transposon mutant library of KT2440 revealed that disruption of the biosynthetic pathway for the siderophore pyoverdine resulted in complete loss of X. fragariae antagonism, suggesting iron competition as a mode of action. Antagonism could be replicated on plate and in culture by addition of purified pyoverdine or by addition of the chelating agents tannic acid and dipyridyl, while supplementing the medium with iron negated the inhibitory effects of pyoverdine, tannic acid and dipyridyl. When co-inoculated with tannic acid onto strawberry plants, X. fragariae’s ability to cause foliar symptoms was greatly reduced, suggesting a possible opportunity for iron-based management of ALS. We discuss our findings in the context of ‘nutritional immunity,’ the idea that plant hosts restrict pathogen access to iron, either directly, or indirectly through their associated microbiota.

Biological control of bacterial plant diseases with Lactobacillus plantarum strains selected for their broad‐spectrum activity

“…The growing interest in sustainable management of plant diseases caused by Psa, Xap and Xf has stimulated the search for novel BCA. While several bacteria, such as Pseudomonas and Xanthomonas , have been selected for studies thanks to their biocontrol activity against these pathogens, the studies in question only focused on a single pathogen (Biondi, Dallai, Brunelli, Bazzi, & Stefani, ; Henry, Gebben, Tech, Yip, & Leveau, ; Kawaguchi, Inoue, & Inoue, ; Wicaksono, Jones, Casonato, Monk, & Ridgway, ). In this present work, a multi‐disease approach was taken to select antagonistic bacteria with broad‐spectrum activity.…”

Host–Pathogen Interactions between Xanthomonas fragariae and Its Host Fragaria × ananassa Investigated with a Dual RNA-Seq Analysis

“…There is evidence that phytopathogenic bacteria can use iron uptake systems to multiply in the host and to promote infection [85]. A study could already report that iron acquisition was crucial for X. fragariae bacterial growth because an iron deprivation could inhibit X. fragariae growth and symptoms on strawberry plant [86].…”

Genetic and structural determinants on iron assimilation pathways in the plant pathogen Xanthomonas citri subsp. citri and Xanthomonas sp.

“…Further, the analysis of X. translucens proteome for iron-binding proteins revealed that this metal assists on the regulation and function of several secreted proteins linked to its virulence [21]. In X. fragariae, after the disruption of the pyoverdine biosynthetic pathway the bacterium lost its pathogenicity [22].…”