ABSTRACT 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.
Śliżewska et al. (Mon,) studied this question.