Specific inactivation of an antifungal bacterial siderophore by a fungal plant pathogen
Brown root rot disease (BRRD) caused by a soil-born fungal pathogen Phellinus noxius. Nowadays, BRRD has been reported throughout the Americas, Africa, Asia, and Oceania as a crucial cause of tree decline and mortality. In Taiwan, BRRD has become a severe threat to destroy the agricultural, landscape, and forest trees during the last 20 years. Previous reports indicate that more than 200 plant species are hosts of P. noxius. Half of the hosts were reported for the first time from Taiwan. Dr. Yu-Liang Yang's group revealed that P. noxius effectively eliminated the antifungal activity of pyochelin and ent-pyochelin, transforming these siderophores into pyochelin-GA. Pyochelin and ent-pyochelin are siderophores with antifungal activity commonly produced by Pseudomonas and Burkholderia species. Meanwhile, P. noxius accumulated dehydroergosterol peroxide in fungal cells in response to the stress of pyochelin and ent-pyochelin. Those metabolic interactions between bacteria and P. noxius were observed in situ using imaging mass spectrometry. Yang's group further confirmed that pyochelin-GA's iron-chelating ability is significantly dismissed, which might influence bacteria to capture extracellular iron using siderophores. The study demonstrated how fungal phytopathogens compete with the siderophores producer bacteria in the soil environment; meanwhile, it would severely weaken bacterial biocontrol agents' efficacy.