Carotenoid production by Metschnikowia sp.: isolation from environmental samples and optimization of culture...

Carotenoids are valuable natural pigments with antioxidant and health-promoting properties. Growing concerns regarding the toxicity and environmental persistence of synthetic colorants have increased interest in safe and sustainable natural alternatives. Compared with plant-derived carotenoids, microbial production offers several practical advantages, including rapid growth, year-round cultivation, utilization of agro-industrial substrates, and simplified downstream processing. This study aimed to isolate carotenoid-producing microorganisms from environmental samples, identify the most productive isolate, and optimize culture conditions for enhanced carotenoid biosynthesis, with particular emphasis on Metschnikowia sp. Five pigmented isolates were recovered, among which Metschnikowia sp. (100% identity, 90% query coverage; GenBank accession no. MZ622714) exhibited the highest carotenoid production (A450 = 4.2) and was selected for further investigation. Using the Taguchi experimental design, the highest biomass yield (10.67 ± 0.58 mg/mL) was obtained in a medium containing glucose and yeast extract at pH 6 and 20 °C, whereas maximum carotenoid production (6.48 µg/g) was achieved under Molasses and peptone (or the correct optimized medium), at pH 7 and 20 °C. Notably, carotenoid biosynthesis was enhanced under stress-associated conditions rather than those favoring maximal biomass formation. UV-Vis spectroscopy and HPLC analyses confirmed carotenoid production, with a dominant chromatographic peak (retention time ⁓21.4 min) consistent with an astaxanthin-like compound. These findings demonstrate the potential of Metschnikowia sp. as a promising non-conventional yeast for sustainable production of natural carotenoids and provide a foundation for future development of industrial microbial bioprocesses.