Diana Vinchira-Villarraga

The emergence of fungicide resistance in Pyricularia oryzae necessitates searching for efficient biocontrol strains from under-explored environments. This study reports P. oryzae control from the marine sponge-associated Streptomyces albidoflavus PNM-87. Initial screenings revealed that PNM-87 exhibits significant in vitro inhibition against rice blast. Active compounds were characterized by Feature-Based Molecular Networking (FBMN) and SIRIUS as a mixture of surfactin-like lipopeptides including surfactins (BC14, C13, C15) and pumilacidins (B, D/E), representing 82% of the total ion current (TIC). Comparative metabolic profiling in pathogen-supplemented media revealed pathogen-induced changes in the specialized metabolome; PNM-87 upregulated surfactin and pumilacidin B production by up to 200- and 400-fold, respectively. Greenhouse assays confirmed plant protection, reducing rice blast severity in O. sativa plants. This work provides the first evidence of a marine-derived S. albidoflavus strain employing a targeted chemical defence strategy for agricultural pathogen suppression, highlighting the potential of marine actinobacteria as biocontrol agents.

Acute oak decline (AOD) is a complex disease of oak trees ( Quercus spp.) which results in bleeding stem cankers and potential tree mortality. A polymicrobial complex is implicated in causing AOD, of which the most commonly isolated species are Brenneria goodwinii and Gibbsiella quercinecans . Bacteriophages (phages), natural predators of bacteria, can act as biocontrol agents that reduce bacterial infections in trees. In this study, the first phages that lyse B. goodwinii and G. quercinecans , BREN6 and GIB1 phages respectively, were isolated from AOD‐impacted trees. Genomic analyses and transmission electron microscopy showed that BREN6 is a novel phage type with siphovirus morphology, whereas GIB1 possesses characteristics typical of N4‐like phages. While in vitro assays showed that each phage could effectively reduce their hosts' population growth for at least 24 h, application of the phages to either single or dual species communities of B. goodwinii and G. quercinecans in the stems of oak saplings showed that the phages had a minimal impact on their host populations, and in some trees actually resulted in higher bacterial populations. Our data show that the application of these phages does not alter the in planta population dynamics between B. goodwinii and G. quercinecans , and emphasises the importance of assessing phage effectiveness within natural settings.

Long term chronic infections of plants by bacterial pathogens are largely unknown. Understanding how pathogens adapt during chronic infection provides a key insight to pathogen evolutionary strategy both for persistence and survival, but also for potential future outbreaks. Pseudomonas savastanoi pv. fraxini ( Psf) , a member of phylogroup 3 within the Pseudomonas syringae species complex, causes canker disease in European ash ( Fraxinus excelsior ). Infections persist for years within the bark parenchyma, where bacteria are enclosed in cavities that contribute to the gradual expansion of host periderm. This pathosystem therefore provides an opportunity to examine pathogen evolution in a long-lived, largely unmanaged host. We combined population genomics and phenotypic analysis of 124 Psf strains collected from six sites across the UK. Phylogenetic analysis revealed a highly clonal population, with only 833 core genome SNPs across a 5.3 Mb genome, and a relatively small accessory genome largely shaped by gain and loss of large mobile genetic elements. Despite this limited genomic diversity, mutations were enriched in regulatory genes, including two-component systems, chemotaxis proteins, and cell envelope-associated loci. Notably, the global regulator gacA/S was independently mutated multiple times within the same clonal lineage. These mutations, typically small deletions, were associated with changes in motility, nutrient utilisation, stress tolerance, and virulence across genetic backgrounds. As a result, phenotypic heterogeneity was observed within otherwise clonal populations, including within individual lesions. These findings indicate that repeated mutation of regulatory systems represents a key mechanism of adaptation in this chronic plant–pathogen interaction, enabling phenotypic diversification despite limited sequence divergence. This study provides a microevolutionary perspective on P. syringae populations in the phyllosphere and highlights the role of regulatory variation in the evolution of low-virulence, ecologically restricted pathogens.

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. In addition, 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 Cladonia 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. In addition, compounds absent in Peltigera , like anthracene, might serve as a carbon source inhibitor like Bacillus velezensis .

Introduction: Tree bacterial diseases are a threat in forestry due to their increasing incidence and severity. Understanding tree defence mechanisms requires evaluating metabolic changes arising during infection. Metabolite extraction affects the chemical diversity of the samples and, therefore, the biological relevance of the data. Metabolite extraction has been standardized for several biological models. However, little information is available regarding how it influences wood extract’s chemical diversity. Objectives: This study aimed to develop a methodological approach to obtain extracts from different tree species with the highest reproducibility and chemical diversity possible, to ensure proper coverage of the trees’ metabolome. Methods: A full factorial design was used to evaluate the effect of solvent type, extraction temperature and number of extraction cycles on the metabolic profile, chemical diversity and antibacterial activity of four tree species. Results: Solvent, temperature and their interaction significantly affected the extracts’ chemical diversity, while the number of extraction cycles positively correlated with yield and antibacterial activity. Although 60% of the features were recovered in all the tested conditions, differences in the presence and abundance of specific chemical classes per tree were observed, including organooxygen compounds, prenol lipids, carboxylic acids, and flavonoids. Conclusions: Each tree species has a unique metabolic profile, which means that no single protocol is universally effective. Extraction at 50 °C for three cycles using 80% methanol or chloroform/methanol/water showed the best results and is suggested for studying wood metabolome. These observations highlight the need to tailor extraction protocols to each tree species to ensure comprehensive metabolome coverage for metabolic profiling.

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 .