Effect of light intensity and wavelength on carotenoid profiles in mixed cultures of purple phototrophic bacteria

Abstract

Purple phototrophic bacteria (PPB) have strong potential for applications such as protein-rich animal feed, with carotenoids providing added immune-nutritional value. This study investigated carotenoid profiles in PPB mixed cultures under varying light conditions, focusing on individual carotenoid quantification using advanced analytical techniques, rather than relying on total carotenoid estimates or spectral inference alone. Lycopene, 3,4-dihydrorhodopin, and rhodopin were consistently identified as the major carotenoids across conditions. Low-light (1.7 W m^-2) increased both lycopene (5.1 mg gVS^-1) and the total carotenoid content compared to higher intensities (2 mg gVS^-1 at 33.1 W m⁻²). Infrared light alone promoted higher carotenoid production compared to its combination with other wavelengths. The capacity to influence both the quantity and composition of carotenoids opens new possibilities to optimise PPB biomass for targeted feed and biotechnology applications, where individual carotenoids provide distinct nutritional and functional benefits.