Abstract
Microorganisms form complex ecological networks of interactions, with secondary metabolites (SMs) playing a crucial role in microbial communication. This study explored the cocultivation of marine fungi Alternaria alternata and Nigrospora sphaerica, uncovering significant SM production changes. The biosynthetic gene clusters (BGCs) and transcription factor aohR in marine A. alternata were activated, leading to enhanced production of alternariol (AOH), a compound inhibiting fungal competitors, whereas the activation was not present in the coculture of terrestrial strains of A. alternata. Transcriptomic and metabolic analyses further revealed that reactive oxygen species (ROS) play a crucial role as signaling molecules in these marine fungal interactions. Elevated ROS levels triggered the upregulation of oxidative stress response genes in marine A. alternata, regulating the expression of aohR, which subsequently induced the biosynthesis of AOH. These findings highlight a unique defensive strategy in marine fungi, offering insights into their ecological roles and potential antibiotic development. IMPORTANCE: Marine fungi are an important source of natural products, and many marine-derived secondary metabolites have been found to exhibit significant bioactivities, including antibacterial, antiviral, and anticancer properties. Cocultivation is a simple and effective method for discovering bioactive compounds. However, whether marine-derived and terrestrial-derived microorganisms exhibit differential response mechanisms under co-culture conditions remains unexplored. Our study details how cocultivation of marine fungi triggers the activation of biosynthetic gene clusters (BGCs) and leads to an increase in active secondary metabolites (SMs), which may contribute to the future development of antibiotics or anticancer drugs. Furthermore, our findings reveal that reactive oxygen species (ROS) function as specific signaling molecules in marine fungal-fungal interactions, offering novel insights into the evolutionary strategies of fungi in marine ecosystems.