Unveiling the diversity, ecology, and biotechnological potential of culturable marine yeasts in Western Mediterranean coastal ecosystems.

Coastal ecosystems are dynamic environments characterized by strong seasonal variability in physicochemical parameters and biological communities. In the western Mediterranean, the Region of Murcia (southeastern Spain) is characterized by notable biodiversity and ecological heterogeneity, encompassing diverse habitats, including rocky shores, sandy beaches, seagrass meadows, and the Mar Menor, one of Europe's largest hypersaline lagoons. Within these systems, marine yeasts play critical ecological roles in organic matter recycling and produce metabolites of biotechnological and medical interest. This study presents the first comprehensive survey of culturable marine yeasts from the Mediterranean coast of the Region of Murcia. From seawater and sediment samples, 415 strains were identified via internal transcribed spacer (ITS) and large subunit (LSU) rDNA sequencing, revealing 90 species across 44 genera, including 78 known taxa and 12 potentially novel ones. Most isolates were assigned to the phylum Ascomycota (62%), primarily distributed among the classes Pichiomycetes, Dothideomycetes, Saccharomycetes, and Dipodascomycetes, whereas Basidiomycota accounted for the remaining 38%, mainly comprising the classes Tremellomycetes and Microbotryomycetes. The genera most represented in both seawater and sediment were Rhodotorula and Candida, and approximately 10% of the isolates corresponded to stress-tolerant black yeast-like fungi (Aureobasidium spp., Hortaea werneckii, Exophiala oligosperma, and Zalaria alba), a group notable for its taxonomic novelty and valuable biotechnological traits. Culturable yeast assemblages displayed pronounced spatiotemporal variability, with diversity generally increasing during milder seasons and in areas influenced by anthropogenic activity, suggesting the combined effect of natural gradients and human-driven alterations. Representative strains exhibited broad enzymatic capabilities, producing extracellular cellulases, proteases, xylanases, amylases, chitinases, and pectinases, underscoring their ecological role in organic matter turnover and nutrient cycling. The findings provide novel insights into the taxonomic composition and metabolic potential of marine yeasts recovered from the Mediterranean Sea and set the basis for their future exploitation in industrial and environmental biotechnology.