Extremophiles are of significant scientific interest due to their unique adaptation to harsh environmental conditions and their potential for diverse biotechnological applications. Among these extremophiles, filamentous fungi adapted to high-salt environments represent a new and valuable source of enzymes, biomolecules, and biomaterials. While most studies on halophiles have focused on bacteria, reports on filamentous fungi remain limited. This review compiles information about salt-adapted fungi and details their distribution, adaptation mechanisms, and potential applications in various societal areas. Understanding the adaptive mechanisms of halophilic fungi not only sheds light on the biology of extremophilic fungi but also leads to promising biotechnological applications, including the development of salt-tolerant enzymes and strategies for bioremediation of saline habitats. To fully realize this potential, a comprehensive understanding of their ecology, diversity and physiology is crucial. In addition, understanding their survival mechanisms in saline environments is important for the development of astrobiology. The significant potential of applications of halophilic fungi is highlighted.

In recent years, there has been increasing interest in the study of extremophilic microorganisms, which include halophiles and halotolerants. These microorganisms, able to survive and thrive optimally in a wide range of environmental extremes, are polyextremophiles. In this context, one of the main reasons for studying them is to understand their adaptative mechanisms to stress caused by extreme living conditions. In this paper, a fungal strain Penicillium chrysogenum P13, isolated from saline soils around Pomorie Lake, Bulgaria, was used. The effect of elevated concentrations of sodium chloride on the growth and morphology as well as on the physiology of the model strain was investigated. P. chrysogenum P13 demonstrated high tolerance to NaCl, showing remarkable growth in liquid and agar media. In order to establish the relationship between salt- and oxidative stress, changes in the cell biomarkers of oxidative stress, such as oxidatively damaged proteins, lipid peroxidation, and levels of reserve carbohydrates of the studied strain were evaluated. The involvement of antioxidant enzyme defense in the adaptive strategy of the halotolerant strain against elevated NaCl concentrations was investigated.

Antimicrobial resistance represents one of the most critical public health challenges of the 21st century. The emergence of multidrug resistance (MDR) in bacterial and fungal pathogens to diverse chemical agents severely impedes the effective treatment of diseases such as cancer and systemic infections. The rapid escalation of microbial resistance underscores the urgent need for the discovery of novel antimicrobial agents and innovative approaches to drug development. In both clinical and industrial contexts, the identification of new antibiotics and antifungals remains pivotal for pathogen control. Current research efforts focus on the development of alternative formulations that offer high efficacy, reduced resistance potential, minimal side effects, and synergistic interactions, particularly those derived from natural sources. Filamentous fungi originating from extreme environments have evolved to thrive under harsh conditions, making them promising reservoirs of bioactive metabolites with unique structural and functional properties. These fungi exhibit potent antimicrobial activity through diverse mechanisms that disrupt essential cellular processes in pathogens. Despite their remarkable potential, the bioprospecting of extremophilic filamentous fungi for drug development remains underexplored. This highlights the necessity for expanded research into the efficacy and safety of their derived compounds. This review aims to emphasize the capacity of extremophilic fungi to produce antimicrobial agents, elucidate resistance mechanisms, characterize fungal bioactive extracts, and analyze their molecular actions in the context of their extreme ecological niches.

Air pollution remains one of the most urgent global challenges, affecting both public health and environmental integrity, with its severity escalating in parallel with industrialization and urban expansion. Defined as the presence of harmful substances in the atmosphere, air pollution poses risks to human health and disrupts the development of plant and animal life. Urban areas, particularly large cities, frequently exhibit pollutant concentrations that exceed safety thresholds established by the World Health Organization (WHO). This study presents a comprehensive analysis of airborne fungal microbiota in two distinct districts of Sofia, Bulgaria: the highly urbanized city center (Orlov Most) and a less urbanized southwestern area (New Bulgarian University, Ovcha Kupel). Weekly fluctuations in mold spore abundance were monitored, revealing elevated contamination levels on Fridays, likely due to intensified vehicular traffic preceding weekends and public holidays. Taxonomic identification of dominant mold species was conducted using both classical and molecular genetic methods. The isolated fungal strains predominantly belonged to the phylum Ascomycota (80%), with Talaromyces and Alternaria emerging as the most prevalent genera. Additionally, antifungal susceptibility testing indicated that most isolates were sensitive to commonly used antifungal agents, although resistance was observed in two strains of Talaromyces wortmannii. These findings underscore the significance of fungal bioaerosols in urban air quality assessments and highlight the need for targeted monitoring and mitigation strategies.

Oxidative stress poses significant challenges for fungi inhabiting extreme environments. Elevated salinity frequently induces the excessive production of reactive oxygen species (ROS), which can damage cellular components and impair growth. In response, fungi—common inhabitants of extreme environments—activate coordinated adaptive mechanisms, including antioxidant defense systems and other stress-related pathways. In the present study, a newly isolated strain, Trichoderma afroharzianum B2.2, obtained from the poorly studied saline habitat of Atanasovsko Lake (Bulgaria), was investigated. The cellular response of this moderately halotolerant strain to increased salinity was characterized. Biomarkers of oxidative stress were evaluated, and the involvement of key enzymes from glycolysis and the pentose phosphate pathway in the strain’s adaptation to elevated salinity was examined. Understanding adaptations to salt environments is crucial not only for elucidating fungal survival mechanisms under extreme conditions but also for their potential applications in biotechnology, ecology, and food safety, particularly in the context of increasing ecosystem salinization and climate change.

Efficient decomposition of lignocellulosic biomass composed of cellulose, hemicellulose, and lignin is vital for sustainable life-support systems in long-duration space missions. Fungi offer a promising solution due to their adaptability, low maintenance, and enzymatic ability to break down complex plant materials. Their enzymes, such as cellulases and lignin-degradingenzymes, convert biomass into fermentable sugars and aromatic compounds, which can be used to produce biofuels, bioplastics, or serve as inputs in closed-loop systems. Fungal strains isolated from woody species, fungal isolates from sawdust and wood surface, and five fungal consortia were tested for cellulase and lignolytic enzyme production. Three fungal strains and the natural consortia were selected as the most promising for the biodegradation of lignocellulosic wastes generated during manned spaceflights.