Salty environments are widely known to be inhospitable to most microorganisms. For centuries salt has been used as a food preservative, while highly saline environments were considered uninhabited by organisms, and if habited, only by prokaryotic ones. Nowadays, we know that filamentous fungi are widespread in many saline habitats very often characterized also by other extremes, for example, very low or high temperature, lack of light, high pressure, or low water activity. However, fungi are still the least understood organisms among halophiles, even though they have been shown to counteract these unfavorable conditions by producing multiple secondary metabolites with interesting properties or unique biomolecules as one of their survival strategies. In this review, we focused on biomolecules obtained from halophilic filamentous fungi such as enzymes, pigments, biosurfactants, and osmoprotectants.

This study investigated agricultural saline soils collected from distinct pedoclimatic profiles from Poland and Italy. Twelve fungal strains from Italy and 9 from Poland were identified and tested for halotolerance, extracellular enzyme production, biosurfactant potential, and mycotoxin production. The tested strains were affiliated to 8 genera, with Aspergillus and Penicillium being the most predominant. All tested strains were confirmed to be good producers of at least one of the analyzed hydrolytic enzymes, with cellulase being the most frequently produced. Notably, Ramularia mali FF1 was the best producer of the tested extracellular enzymes and showed the highest enzymatic activity for amylase, cellulase, chitosanase, pectinase and xylanase among all strains. A hemolytic assay was implemented to evaluate the potential for biosurfactant production in media supplemented with various sodium chloride concentrations. Among 21 tested strains, 14 demonstrated hemolytic activity at 5% NaCl. Based on the results, Acremonium sclerotigenum FF3 was selected to perform biosurfactant analysis. Mycotoxin screening revealed that Penicillium canescens S10 was the only producer of any examined mycotoxin, with 5.759 μg/mL concentration of ochratoxin A. This research underscores the varied enzymatic and biosurfactant capabilities of halophilic fungi adapted to saline soils and highlight the biotechnological potential of these organisms and environments.

Microbial pigment production is often a physiological response to environmental stress, including salinity, oxidative stress, and nutrient limitation. In this study, we investigated Aspergillus tubingensis FF14, a filamentous fungus isolated from naturally salinized coastal soil, periodically penetrated by seawater. This strain produced a distinctive orange intracellular pigment, which was identified via ultra-high-performance liquid chromatography coupled to diode array detection and electrospray ionization mass spectrometry as a mixture of three xanthophylls: violaxanthin, antheraxanthin, and neoxanthin. To date, this is the first documented case of xanthophyll biosynthesis in an Aspergillus species. Additionally, the antioxidant potential of the extracted pigment mixture was evaluated. Optimization experiments revealed that maximal pigment yield occurred at pH 3, 30°C, with 5% (vol/vol) sodium chloride, and 30% malt extract medium volume. Genome sequencing and annotation revealed biosynthetic gene clusters with domains characteristic of lycopene cyclase and phytoene synthase, indicating involvement in early steps of C40 carotenoid biosynthesis. Although biosynthetic gene clusters that are potentially linked to carotenoid biosynthesis were identified, the specific mechanisms responsible for xanthophyll biosynthesis in A. tubingensis FF14 remain to be elucidated. These findings provide new insights into fungal carotenoid metabolism and demonstrate the potential of A. tubingensis FF14 as a sustainable source of carotenoid pigments. IMPORTANCE: Microorganisms living in extreme environments frequently produce compounds with protective value against environmental stressors. Although these natural products have potential practical value, many remain undiscovered. We identified a halophilic fungus, Aspergillus tubingensis FF14, isolated from saline soil that produces bright orange pigments belonging to the xanthophyll family, a group of carotenoids with antioxidant potential. This is the first report on xanthophyll production in this genus. We showed that salt stress enhanced pigment production and optimized culture conditions to increase pigment yield. Genome analysis identified the genes that are most likely responsible for carotenoid biosynthesis, linking metabolite production with genetic potential. These findings expand current knowledge of fungal metabolites and demonstrate that extremophilic fungi may be promising and sustainable sources of valuable natural pigments.