Antagonistic effect of 7-hydroxytropolone and its substitutes against Dickeya solani

Abstract

Dickeya species are major plant pathogenic bacteria worldwide, with Dickeya solani (D. solani) posing a key threat to potato crops, which rank fourth among the most cultivated food crop globally. D. solani is responsible for blackleg disease, causing significant yield and quality losses in seed potato production. Current control options, whether phytochemicals or biocontrol strategies against blackleg disease, remain limited. However, the potato rhizosphere bacterium Pseudomonas PA14H7 has shown effective antagonism against D. solani via the production of 7-hydroxytropolone (7-HT). This molecule was identified in the filtered supernatant of Pseudomonas PA14H7 (FS-PA14H7) complexed with iron. Herein, we demonstrate that the activity of 7-HT is strongly linked to its ability to chelate iron, thereby inhibiting the growth of D. solani through iron deprivation. Given the challenges associated with synthesizing 7-HT, alternative commercially available molecules with the same elemental composition and bearing functional groups such as catechol, phenol or carboxylic acid were screened for their ability to chelate iron using computational calculations and mass spectrometry techniques (UPLC-HRMS and MS/MS). Then, their antibacterial activity against D. solani and other Soft Rot Pectobacteriaceae was evaluated and compared with the one of 7-HT. Three candidates 2,3, 2,4 and 2,5- dihydroxybenzaldehydes were identified as potential substitutes, presenting promising biocontrol solutions for managing potato blackleg disease.