Characterization of metabolomic differences in peanut worm Sipunculus nudus between breeding and nonbreeding seasons

Peanut worm, Sipunculus nudus, is an important economic and ecological species. This study aims to characterize differences in the coelomic fluid of S. nudus between breeding and nonbreeding seasons. Animals were obtained in July and November. The diameter of oocytes was measured and analyzed. Results showed that the number of oocytes formed a primary peak at a diameter of approximately 160 mu m in July, while almost all oocytes were below 50 mu m in November. A metabolomics approach based on LC-MS and GC-MS was used to investigate differences in coelomic fluid and gain insights into the mechanisms underlying the oocyte development of S. nudus. In the metabolomics assay, 44 and 32 significantly differential metabolites were obtained via LC-MS and GC-MS (VIP > 1 and P < 0.1), respectively. S. nudus changed its metabolic status under different development conditions. The analysis of further integrated key metabolic pathways showed that S. nudus possessed different capabilities for valine, leucine, and isoleucine biosynthesis; phenylalanine, tyrosine, and tryptophan biosynthesis; aminoacyl-tRNA biosynthesis; butanoate metabolism; tyrosine metabolism; alanine, aspartate, and glutamate metabolism; galactose metabolism; and ubiquinone and other terpenoid-quinone biosynthesis between breeding and nonbreeding seasons. S. nudus may exhibit high anabolic ability to store nutrients and hold the high activity of neurotransmitter precursors to regulate oocyte development during the breeding season. This metabolomics study is the first to identify crucial metabolites and key pathways to understand the metabolic mechanism of oocyte development. The results provide theoretical basis for artificial breeding of S. nudus.