Abstract
Salterns are hypersaline environments that are inhabited by diverse halophilic microorganisms, including fungi. In this study, we isolated a fungal strain SK1-1 from a saltern in the Republic of Korea, which was identified as Asperillus reticulatus. This is the first reported saline-environment-derived A. reticulatus that belongs to the Aspergillus penicillioides clade and encompasses xerophilic fungi. SK1-1 was halophilic, obligately requiring NaCl for growth, with a maximum radial growth of 6%–9% (w/v) NaCl. To facilitate the biotechnological application of halophilic fungi, we screened the SK1-1 strain for proteolytic activity. Proteases have widespread applications in food processing, detergents, textiles, and waste treatment, and halophilic proteases can enable protein degradation in high salt environments. We assessed the proteolytic activity of the extracellular crude enzyme of SK1-1 using azocasein as a substrate. The crude protease exhibited maximum activity at 40–50 °C, pH 9.5–10.5, and in the absence of NaCl. It was also able to retain up to 69% of its maximum activity until 7% NaCl. Protease inhibitor assays showed complete inhibition of the proteolytic activity of crude enzymes by Pefabloc® SC. Our data suggest that the halophilic A. reticulatus strain SK1-1 produces an extracellular alkaline serine protease.
Highlights
Accepted: 23 December 2021Microorganisms in extreme environments have gained increasing scientific attention because they serve as valuable models of functional evolution and have potential biotechnological applications [1,2]
When the fungi were cultured on potato dextrose agar (PDA) supplemented with 0%, 5%, and 10%
NaCl to isolate pure colonies, we observed that one strain, designated SK1-1, did not grow on PDA without NaCl supplementation
Summary
Microorganisms in extreme environments have gained increasing scientific attention because they serve as valuable models of functional evolution and have potential biotechnological applications [1,2]. During physiochemical adaptation to harsh environments, they can obtain unique genetic and metabolic traits, as compared to microorganisms in general environments [3]. Solar salterns are extreme hypersaline environments that are inhabited by a diverse range of microorganisms, including archaea, bacteria, and fungi [4]. Several halophilic and halotolerant fungal species isolated from solar salterns have been previously reported. Fungi prevalently isolated from salterns include black yeasts (Hortaea werneckii and Aureobasidium pullulans), Aspergillus, Penicillium, and Cladosporium species [5,6,7]. Wallemia ichthyophaga and Aspergillus penicillioides have been reported as obligate halophilic fungi isolated from salterns [8,9]
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