Optimization of melanin pigment production from the halotolerant black yeast Hortaea werneckii AS1 isolated from solar salter in Alexandria

Background Melanins are one of the magnificent natural pigments synthesized by a wide range of microorganisms including different species of fungi and bacteria. Marine black yeasts appear to be potential prospects for the synthesis of natural melanin pigment. As a result, the goal of this research was to isolate a marine black yeast melanin-producing strain and improve the culturing conditions in order to maximize the yield of such a valuable pigment. Results Among five locally isolated black yeast strains, the only one that demonstrated a potent remarkable melanin pigment production was identified using ITS rDNA as Hortaea werneckii AS1. The extracted pigment's physiochemical characterization and analytical investigation with Ultraviolet-Visible (UV) spectrophotometry, Fourier Transform-Infrared spectroscopy (FTIR), and Scanning Electron Microscope (SEM) confirmed its nature as a melanin pigment. The data obtained from the polynomial model's maximum point suggested that CaCl2, 1.125 g/L; trace element, 0.25 ml/L; and a culture volume 225 mL/500 mL at their optimal values were the critical three elements impacting melanin production. In comparison with the baseline settings, the response surface methodology (RSM) optimization approach resulted in a 2.0 - fold improvement in melanin output. Conclusions A maximum melanin yield of 0.938 g/L proved the halotolerant H. werneckii AS1 potentiality as a source for natural melanin pigment synthesis 'when compared to some relevant black yeast strains' and hence, facilitating its incorporation in a variety of pharmaceutical and environmental applications.