Ramirez Carrera, N. | bioRxiv Science

bioRxiv2024

Exploring the Exclusive Isolation of Pseudomonas syringae in Peltigera Lichens via metabolite analysis and growth assays

The specific association of the potentially plant-pathogenic Pseudomonas syringae with Peltigera lichens raises questions about the factors driving this host specificity. To explore this, the metabolic profile of seven lichen species belonging to three genera (Cladonia, Peltigera, and Stereocaulon) was analysed using LC-MSMS. Additionally, we assessed the growth of P. syringae strains in media supplemented with extracts from each lichen species. This revealed that Peltigera exhibits lower metabolite richness compared to other genera, but shows a higher chemical investment in specific compounds. Growth kinetics showed comparable P. syringae growth across lichen-supplemented media, except for C. arbuscula and Cladonia sp., where the former exhibited lower growth rates. Inhibition assays with lichen extracts showed no inhibition of P. syringae. The lichen metabolome is predominantly composed of lipids and organic acids. Furthermore, specific compounds, such as aminoglycosides, may facilitate P. syringae presence in Peltigera by inhibiting Bacillus subtilis and other antagonists. Additionally, compounds absent in Peltigera, like anthracene, might serve as a carbon source inhibitors like B. velezensis.

microbiology↗

bioRxiv2023

From lichens to crops: Pathogenic potential of Pseudomonas syringae from Peltigera lichens is similar to world-wide epidemic strains

The presence of bacteria belonging to the Pseudomonas syringae complex (P. syringae) in the natural vegetation of several Icelandic habitat types has been recently reported, raising questions about the risk to Icelandic crops, particularly given the expected increase in agricultural activity due to climate warming. This study takes advantage of Icelands unique characteristics and the discovery of P. syringae in Peltigera lichens to gain a better understanding of the potential risk posed by this newly discovered ecological niche. The main objective is to evaluate the pathogenic potential and fitness in crops of P. syringae strains isolated from Peltigera lichen sampled in Iceland, focusing on strains that belong to phylogroups 1 and 2, which commonly contain epidemic strains. The results indicate that P. syringae isolated from Icelandic Peltigera lichen have a comparable fitness to epidemic strains in eight out of ten tested plant species. Furthermore, pathogenicity assessment on three plant species highlighted that certain strains also caused similar symptoms and disease severity compared to epidemic strains. These findings provide valuable insights into the potential risks posed by P. syringae from Icelandic natural habitats and illustrate how strains from these habitats have a wide pathogenic potential to crops without having encountered these crops in the last several thousand years of their presence in Iceland.

microbiology↗