Phenotypic and transcriptomic insights into chloride tolerance mechanisms in the mangrove wetland-derived fungus Aspergillus aculeatus

Mangrove wetland-derived Aspergillus aculeatus have emerged as promising bioinoculants for bioremediation of high chloride wastewater, yet their molecular adaptation mechanisms under salt stress remain poorly understood. This study integrates phenotypic characterization, transcriptomic profiling and weighted gene co-expression network analysis (WGCNA) to comprehensively elucidate the multilayered adaptive responses of A. aculeatus strain H7 to increasing NaCl concentrations (0%, 7.5% and 15% w/v). Our results demonstrated that salt stress significantly delayed the transition from conidia to hyphae in a dose-dependent manner. Ultrastructural analysis revealed pronounced alterations in salt-stressed cells compared with untreated controls. In parallel, physiological analyses revealed substantial cell wall remodeling, evidenced by increased chitin content and total polysaccharide accumulation. Compatible solutes were significantly upregulated, with glycerol increased from 1.12 to 11.60 mg/g dry weight. In contrast, intracellular ATP levels progressively declined, whereas oxidative stress indicators increased substantially with salinity. Transcriptomic analysis identified 4,217 differentially expressed genes, while KEGG enrichment analysis revealed significant modulation of pathways involved with amino acid, carbohydrate, lipid and energy metabolism, as well as oxidative stress responses. Collectively, these findings suggest that A. aculeatus H7 adapts to hyperosmotic stress through coordinated regulation of compatible solute accumulation, cell wall remodeling, metabolic reprogramming and antioxidant defense systems. This study provides new insights into fungal salinity adaptation mechanisms and offers a theoretical basis for the development of stress-resilient fungal strains for high-chloride wastewater bioremediation, with potential extension to saline–alkali soil remediation.