In this study, the pink yeast Rhodotorula sp. strain ATL72 was isolated from salt marches near Mediterranean Sea, Egypt. From phylogenetic analysis, the isolated strain ATL72 was closely related to Rhodotorula bloemfonteinensis EU075187 by similarity of 40%. The biological synthesis of nanosilver (AgNPs) using the marine pink yeast Rhodotorula sp. strain ATL72 was established. The UV-Visible spectral analysis confirmed the synthesis of AgNPs showing a characteristic peak around 400-500 nm. TEM analysis not only confirmed the synthesis of AgNPs but also described the spherical and oval shaped nanoparticle besides size measurements ranged from 8.8 to 21.4 nm. The biosynthesized AgNPs showed a strong antimicrobial activity by causing a complete inhibition of growth for a wide range of Gram positive and Gram negative bacteria as well as fungi with low MIC value. In conclusion, the pink yeast Rhodotorula sp., strain ATL72 isolated from Egypt is a promising new biological source for the synthesis of silver nanoparticles having a potent antimicrobial activity against a wide range of pathogenic bacteria and fungi.

Rhodotorula yeasts which are known as carotenogenic yeasts have a great industrial value due to their ability to produce carotenoids. In particular, the isolated yeast Rhodotorula sp. (strain ATL72) has been reported to be a promising producer of high concentrations of carotenoids. A combination of central composite design (CCD) and Plackett–Burman (PB) design was used to optimize carotenoids produced by this yeast. The optimum production of carotenoids was completed when the yeast was grown in a production medium composed of 3.7 g/L malt extract, 7.7 g/L fructose, 9 g/L urea, 35 g/L NaCl, and 1 g/L yeast extract at 27.5 °C, pH 6.7, and 180 rpm. Two batch runs in 1L and 7L bioreactors were conducted which increased the productivity of carotenoid concentration from 21.5 mg/L after 98h of incubation at the level of the shake flask to 229.9 mg/L after 47 h of incubation at the level of 7 L bioreactor. The carotenoid pigment was extracted in dimethylsulfoxide (DMSO), acetone, petroleum ether, and sodium chloride, and subsequently identified and characterized using the following: UV-visible scanning, thin layer chromatography, and gas chromatography/mass spectrometry.