Carotenoid profiling of Mytilus coruscus with unialgal cultures: Insights into biosynthetic pathways in tissues

Abstract The carotenoid profiling of Mytilus coruscus generally depends on the dietary microalgae, and the ingested carotenoids are modified and processed depending on the properties of different tissues. Although much research effort has focused on analyzing carotenoid profiling between microalgae and shellfish, the detailed metabolic pathways of dietary carotenoids in shellfish are poorly understood. In the present study, we carried out feeding experiments with different unialgal cultures (Chaetoceros mulleri and Dicrateria inornata) during the growth stages and examined the carotenoid profiles between the dietary microalgae and the corresponding tissues in order to study the resorption and metabolic transformations of dietary carotenoids in M. coruscus. The results showed that 1) carotenoids mainly occurred in the pre-spawning phase of M. coruscus; the contents of most carotenoids showed the same trends as in dietary microalgae. 2) An association analysis of the total content of carotenoids and relevant gene expression demonstrated that the main tissue for carotenoid synthesis in M. coruscus was the hepatopancreas. The synthetic reactions of the allenic to acetylenic carotenoids pathway and the 4-keto oxidative pathway in M. coruscus coexisted. 3) Quantitative analysis revealed that the carotenoids mytiloxanthin, alloxanthin, and pectenolone containing acetylene groups were selectively assimilated in gonad (69.3–74.1%), mantle (83.2–102%), and muscle (86.9–100%), forming a large percentage of the carotenoids present in those tissues. These results provide new insights into the biosynthetic and metabolic transformation pathways of carotenoids in M. coruscus.