Exploring metabolic interaction between Ophiostoma novo-ulmi and Geosmithia spp

Dutch elm disease (DED), caused by the invasive vascular pathogen Ophiostoma novo-ulmi , one of the most devastating pandemics affecting elms. Within beetle galleries and on elm bark beetle vectors, O. novo-ulmi co-occurs with fungi of the genus Geosmithia , yet the functional significance of this association remains poorly understood. This study investigates metabolic interactions between O. novo-ulmi and Geosmithia spp. using in vitro dual-culture experiments and phenotype microarray analysis to elucidate ecological mechanisms potentially influencing disease development and vector ecology. Dual-culture assays on dH ₂ O agar revealed that O. novo-ulmi exhibited significantly enhanced radial growth rates when cultured in proximity to Geosmithia isolates. Phenotypic microarray analysis revealed distinct metabolic strategies: O. novo-ulmi utilised substrates within 12–24 hours and preferred polyols and simple carbohydrates, while G. pumila adopted a progressive colonisation strategy, ultimately utilising 92 substrates in 90 hours and demonstrating greater utilisation of nitrogen-enriched substrates, nucleosides and complex organic acids. Fungal competitiveness analysis indicated G. pumila superiority, yet O. novo-ulmi showed greater growth facilitation in co-culture, suggesting asymmetric mutualism through non-nutritional mechanisms. These results also suggest that physical proximity between O. novo-ulmi and Geosmithia spp. establishes a localized metabolic interface enabling chemical signaling and nutrient exchange. This mutualistic interaction, demonstrated by the increased growth of O. novo-ulmi in co-culture without suppressing Geosmithia spp., likely confers selective advantages that explain the evolutionary success of their ecological partnership. Within naturally colonised host tissues, such metabolic interaction may enhance pathogen establishment and persistence, with implications for disease epidemiology, beetle vector ecology, and potential disease management strategies.