Exploring Metabolic Interaction between Ophiostoma novo-ulmi and Geosmithia spp.

Abstract Dutch elm disease (DED), caused by the invasive vascular pathogen Ophiostoma novo-ulmi , is 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 subsp. novo-ulmi exhibited significantly enhanced radial growth rates when cultured in proximity to Geosmithia isolates. Phenotypic analysis revealed distinct metabolic strategies: O. novo-ulmi subsp. novo-ulmi utilised substrates within 12–24 h and preferred polyols and simple carbohydrates, while G. pumila adopted a progressive colonization strategy, ultimately utilising 92 substrates in 90 h and demonstrating greater utilisation of nitrogen-enriched substrates, nucleosides and complex organic acids. Co-culture revealed utilization of adenosine and nitrogen-rich compounds, but antagonistic interactions for polyols and amino sugars. Niche overlap analysis showed asymmetric resource partitioning: O. novo-ulmi subsp. novo-ulmi utilized 98% of G. pumila ’s substrates versus 81% reciprocal overlap, while fungal competitiveness analysis indicated G. pumila superiority. The distinct metabolic strategies and complementary patterns of substrate utilisation suggest niche construction and the functional partitioning of resources. These findings provide evidence supporting the hypothesis of a functional association within the DED pathosystem. The results highlight the ecological importance of microbial community complexity in pathogenic interactions and suggest that understanding these multitrophic relationships is essential for the development of effective disease management strategies.