Statistical Medium Optimization for Enhanced Zeaxanthin Production by a Novel Marine Bacterium Lutimonas zeaxanthinifaciens YSD2104T

Abstract

Zeaxanthin is a high-value xanthophyll carotenoid with broad applications in the pharmaceutical and nutraceutical industries, owing to its potent antioxidant properties and its efficacy in preventing age-related macular degeneration. In this study, we systematically optimized the culture conditions and medium composition for Lutimonas zeaxanthinifaciens YSD2104T, a recently isolated marine bacterium, to enhance biomass and zeaxanthin production. Initial optimization via the one-factor-at-a-time (OFAT) approach established the culture conditions at 30 °C, pH 7.0, and 2% (w/v) NaCl. To identify the key nutritional components within the complex Marine Broth (MB), a fractional factorial design (FFD) was employed to screen eleven components. Among these, NaCl, yeast extract, ferric citrate, and peptone were identified as the most significant factors. Specifically, salinity and complex carbon and nitrogen sources significantly enhanced zeaxanthin biosynthesis, whereas ferric citrate primarily contributed to biomass accumulation. Subsequently, response surface methodology (RSM) using a central composite design was applied to determine the optimal concentrations and explore the interactive effects of these four components. The optimized medium containing 20.86 g L−1 NaCl, 2.8 g L−1 yeast extract, 0.02 g L−1 ferric citrate, and 4.01 g L−1 peptone was validated in a 3-L bioreactor (1.5-L working volume). Under these optimized conditions, biomass and zeaxanthin production achieved 1.4-fold and 1.7-fold increases, respectively, compared to the unoptimized MB formulation. These findings demonstrate that statistical optimization is an effective strategy for developing a highly productive fermentation process for zeaxanthin production by L. zeaxanthinifaciens YSD2104T and support further development of this strain as a sustainable marine bioresource.