Melanin antibacterial activity of two new strains, SN1 and SN2, of Exophiala phaeomuriformis against five human pathogens

Melanin is an almost ubiquitous pigment of brown to dark black color synthesized by living organisms. It has excellent potential for application in several fields, especially in pharmaceuticals. Yeasts are known for their ability to synthesize pigments, including melanin. These yeasts are considered black yeasts. However, there is little information on the synthesis of melanin by these yeasts. This work was designed to study the ability of black yeast to produce a diffusible dark pigment on agar. Two strains of black yeast, SN1 and SN2, were isolated from hydrocarbon-polluted soils. Based on morphological, physiological, and molecular analyses, the two strains SN1 and SN2 were identified as new species of the Exophiala phaeomuriformis strain. After pigment extraction, melanin was characterized using UV and Fourier transform infrared spectroscopy. We found that melanin synthesis is strongly affected by light and optimal parameters such as temperature 30°C, salinity between 10 and 30 ppt, and basic pH. Both melanin extracts also showed inhibitory activity against pathogenic germs, and activities were observed on E. coli (33.33 ± 2.88 mm), Pseudomonas aeruginosa (29.33 ± 4.61 mm), and Staphylococcus aureus (24.3 ± 7.65 mm). It was concluded that the melanin of the E. phaeomuriformis strain isolated from oil-polluted soils had high antibacterial activity. This high antibacterial activity could be a suitable source of new antibacterial natural products.