Enhancing Lycopene Biosynthesis in Cereibacter sphaeroides DT.1: Effects of Glutamate and Proline Supplementation and Fermentation Optimization

Lycopene is a natural carotenoid with antioxidation properties. The objective of the present study was to investigate the roles of glutamate and proline in lycopene biosynthesis in a newly isolated purple non-sulfur bacteriumCereibacter sphaeroidesDT.1, under aerobic conditions. This strain contained a distinct CrtI4capable of converting phytoene to lycopene via four-step desaturation. In order to enhance lycopene production, acrtCknockout mutant was constructed via homologous recombination. Supplementation with glutamate or proline to fermentative medium significantly enhanced intracellular lycopene accumulation in wildtype strain by a respective 99.40 ± 0.54% and 101.70 ± 0.49% and in aΔcrtCmutant strain by 38.13 ± 0.15% and 39.83 ± 0.27%, respectively. Differential transcriptomic and metabolomic analyses showed that these promoting effects were associated with downregulation of the expression of the acyclic carotenoid 1,2-hydratase gene, and increased accumulation of lycopene precursors such as pyruvate and acetyl-CoA. The fermentation conditions for lycopene production were optimized through shake flask experiments. Feasibility for lycopene production was confirmed in a fed-batch cultivation process and a high yield of 151.10 ± 0.13 mg/L was achieved. ThisΔcrtCmutant strain exhibited advantages, such as relatively lower oxygen demand and no need for illumination, making it a potentially useful strain for lycopene production under aerobic conditions.