Co-Culture of Auxenochlorella protothecoides and Serratia liquefaciens Promotes Lutein Accumulation

Lutein, a crucial carotenoid with diverse biological roles, is in high demand in the market. Current production predominantly relies on plant extraction, which is hindered by low yield and seasonal limitations. Microalgae, such as Chlorella and Chlamydomonas, known for their efficient lutein production due to high photosynthetic efficiency, rapid growth, and ease of cultivation, still require enhanced yields. This study presents a novel finding that co-cultivating <i>A. protothecoides</i> with <i>S. liquefaciens</i> significantly boosts lutein production. Optimization of carbon and nitrogen sources, nitrogen-to-phosphorus (N:P) ratio, and algal-bacterial inoculation ratio using BG11 medium was systematically conducted. The results indicate that supplementing with 3.0 g/L sodium acetate as the carbon source, 2.0 g/L sodium nitrate as the nitrogen source, sodium dihydrogen phosphate to achieve an N:P ratio of 12:1, and an algal:bacterial inoculation ratio of 10:1, resulted in an <i>A. protothecoides</i> biomass of 21.72 g/L (DWt) and a lutein yield significantly increased to 56.86 mg/g (DWt), a ninefold rise compared to monoculture. This co-cultivation approach offers a promising avenue for sustainable industrial lutein production.