The peanut worm (Sipunculus nudus) is an economically important fishery resource in China. To determine how dietary carbohydrate and protein levels affect the growth performance of juvenile S. nudus and identify the mechanisms underlying observed patterns, five isoenergetic and isolipidic diets with different levels of carbohydrate and protein were formulated and fed to juvenile S. nudus; the experimental groups were referred to as EG1, EG2, EG3, EG4, and EG5, respectively. After 90 days of feeding, S. nudus had significantly lower survival rates when fed D5 compared with other diets (P < 0.05), and the highest survival rate was observed in EG2 individuals. The weight gain rate and specific growth rate were significantly higher in EG2 compared with the other groups (P < 0.05). Metabolomic profiling using liquid chromatography–mass spectrometry revealed 83 significantly differential metabolites (POS: 59; NEG: 24), which were identified via an in-house MS2 database. Pathway analysis indicated that the significantly different metabolites were involved in 22 metabolic pathways (POS: 9; NEG: 13), including tyrosine, phenylalanine, and tryptophan biosynthesis; phenylalanine metabolism; D-glutamate and D-glutamine metabolism; proline and arginine metabolism; aspartate, alanine, and glutamate metabolism; and aminoacyl-tRNA biosynthesis. These analyses implied that the biosynthetic capabilities of juvenile S. nudus were greater in the EG2. The results of this research enhance our understanding of the effects of dietary carbohydrate and protein levels on the growth performance of juvenile S. nudus.
The peanut worm (Sipunculus nudus) is an important economic and ecological fishery resource in China. To determine how S. nudus interacts with its culture environment, in this study, the diversity, composition, and interrelationships of bacterial communities in the intestine, coelomic fluid, and culture environment of S. nudus through high-throughput sequencing using the Illumina HiSeq sequencing platform. Alpha diversity analysis showed that the highest bacterial community richness and diversity were found in the sediments. Species annotation revealed that Proteobacteria dominated in all samples (48.92%–58.36%), and the other dominant phyla were highly variable, indicating a certain independence between the environment and the composition of the bacterial community of S. nudus. The coelomic fluid of S. nudus contained high concentrations of Bacillus and could be a source of potential probiotic bacteria for isolation and culture. Cluster and operational taxonomic unit Venn diagram analyses showed that the bacterial community composition in the intestine was more similar to that in the sediments compared with water. The predicted functional analysis of bacterial communities indicated that the functions of bacterial communities in the different surrounding environment were highly similar and involved in various aspects, such as membrane transport, amino acid metabolism, carbohydrate metabolism, and replication and repair. Our findings have important implications on the establishment of sustainable microecological regulation and management strategies for S. nudus culture and provide a reference for the development and utilization of probiotic bacteria.
Germinal vesicle (GV) breakdown (GVBD) is an important event in the maturation of oocytes. This process is also a prerequisite for the fertilization of many invertebrates. In Sipunculus nudus, the gonads cannot be observed with the naked eye. Oocytes develop freely in the coelomic fluid and separated easily. Thus, they are a good material for studying invertebrate GVBD. We isolated and obtained samples of oocytes from GV and GVBD phases of S. nudus and constructed two oocyte transcriptomes. Transcriptome analysis identified 14,170 differentially expressed unigenes (DEUs). Gene Ontology (GO) enrichment analysis showed that 69 GO terms were significantly enriched, and 6 GO terms including integral component of membrane (GO: 0016021), nuclearus (GO: 0005634), protein kinase activity (GO: 0004672), protein tyrosine phosphatase activity (GO: 0004725), spindle pole (GO: 0000922) and microtubule organizing center (GO: 0005815) were closely related to GVBD. We identified 31 DEUs associated with the GVBD process including M‐phase inducer phosphatase 2 (CDC25B), 5‐hydroxytryptamine receptor (5‐HTR) and calcium‐transporting ATPase sarcoplasmic/endoplasmic reticulum type (SERCA). The results support the view that hormonal action, calcium regulation, phosphorylation and spindle microtubule action may participate in the process of GVBD. This research presented the development process of S. nudus oocytes and provided valuable materials for the GVBD in other invertebrates.
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