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.

Antarctica, with its harsh environmental conditions, is home to a wide variety of microorganisms, including filamentous fungi. The survival of Antarctic mycoflora has led to increasing interest in their adaptation. Extreme low temperatures, low water availability, frequent freeze–thaw cycles, strong winds, ultraviolet radiation, etc., are all prerequisites for accelerated production of reactive oxygen species (ROS) and the occurrence of oxidative stress (OS). Antarctic fungi have effective mechanisms to cope with the damaging effects of ROS. While the distribution, morphology, physiology, and biotechnological potential of these fungi are well documented, the role of oxidative stress in their adaptation is poorly understood. This has been one of the main research topics of our team for a long time, and a number of papers on our results have been published. This review summarizes the existing literature on the induction of oxidative stress in Antarctic psychrophilic, psychrotolerant, and mesophilic fungi by extreme conditions. The most recent and relevant studies reporting on the relationship between cold stress and OS biomarkers and the damaging effects of ROS on key intracellular biomolecules are presented. The contribution of both enzymatic and non-enzymatic antioxidant defenses to the fungal cell response is discussed.

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.

In order to meet the ever-growing needs of society, modern agriculture must develop sustainable farming and livestock production. Crops need phosphorus, a macronutrient found in soils, but they are only able to utilize small quantities of it. Chemical phosphate fertilizers are ineffective and environmentally harmful. The use of microorganisms (bacteria, yeast, filamentous fungi, and microalgae) that synthesize phytases is a promising and environmentally friendly alternative to chemical fertilizers. Phytases are also needed as feed additives in animal husbandry to overcome phosphorus deficiency for animal growth and development. Phytases are phosphatases that catalyze the release of phosphorus from phytate by stepwise hydrolysis. The broad substrate specificity, optimal pH range, higher thermal stability, and specific efficiency of fungal phytases make them interesting enzymes for agricultural applications. They improve and stimulate the growth and development of plants and animals by releasing inorganic phosphorus and producing siderophores, organic acids, hydrogen cyanide, ammonia, and phytohormones. Phytases are crucial for enhancing phosphorus use in farming and decreasing phosphorus waste’s environmental effects. This paper addresses key challenges in modern farming, such as the inefficient utilization of phosphorus from soil and the environmental harm caused by chemical fertilizers, and provides a comprehensive overview of recent advances in the research of fungal phytases. Available scientific data have been synthesized to highlight the potential of phytase use in agriculture. This review outlines key areas for future research, including the development of phytase variants with improved functionality. The potential integration of fungal phytases into sustainable agricultural practices is underlined, in contrast to previously published work focused primarily on their biochemical properties. The review offers new insight into the possible applications of micromycete phytases as a critical factor for sustainable agriculture in the future.

Catalase (CAT) is an enzyme involved in the first line of cellular antioxidant defense. It plays a key role in the protection of a wide range of Antarctic organisms against cold stress. Extracellular catalase is very rare and data on it are extremely scarce. The aim of the present study was to select an efficient producer of extracellular catalase from amongst Antarctic filamentous fungi. Sixty-two Antarctic filamentous fungal strains were investigated for their potential ability to synthesize intracellular and extracellular CAT. The Antarctic strain Penicillium rubens III11-2 was selected as the best producer of extracellular catalase. New information on the involvement of the extracellular antioxidant enzymes superoxide dismutase and CAT in the response of filamentous fungi against low-temperature stress was obtained. An efficient scheme for the purification of CAT from culture fluid was developed. An enzyme preparation with high specific activity (513 U/mg protein) was obtained with a yield of 19.97% and a purification rate of 98.4-fold. The purified enzyme exhibited maximal enzymatic activity in the temperature range of 5–40 °C and temperature stability between 0 and 30 °C, therefore being characterized as temperature sensitive. To our knowledge, this is the first purified extracellular cold active catalase preparation from Antarctic filamentous fungi.

Fungal infections are a significant global public health challenge because of their widespread occurrence, morbidity, and profound social and economic consequences. Antifungal resistance is also an increasing concern, posing a substantial risk to public health. There is a growing interest in searching for new antifungal drugs isolated from natural sources. This study aimed to evaluate the antifungal activity of novel mollusk fractions against fungal strains resistant to nystatin and amphotericin B. In addition, the role of oxidative stress in the mechanism of damage was determined. The mucus from the garden snail Cornu aspersum (MCa/1-20) and the hemolymph fraction from the marine snail Rapana venosa (HLRv/3-100) were obtained and characterized via 12% sodium dodecyl sulfate–polyacrylamide gel electrophoresis (SDS-PAGE) and mass spectrometric -analyses. The results demonstrate that the spores and biomass of both mollusk fractions have a significant fungicidal effect against Penicillium griseofulvum, and Aspergillus niger. Compared to the control group, the release of intracellular proteins and reducing sugars was significantly increased in the treated groups. The data showed increased levels of oxidative stress biomarkers (lipid peroxidation and oxidatively damaged proteins) and a downregulated antioxidant enzyme defense, corresponding to increased antifungal activity. To our knowledge, this is the first study evaluating oxidative stress as a factor in mollusk fractions’ antifungal activity.