Evaluation of growth, immune characteristics and gut microbiota of juvenile sea cucumber Apostichopus japonicus fed with fermented feed from Corynebacterium glutamicum

As a kind of green and high quality feed, fermented feed has the activity of promoting growth and improving immunity in aquaculture. The aim of this study was to develop a new liquid fermented feed for the culture of sea cucumber Apostichopus japonicus and evaluate its nutritional value and function. After the commercial feed of the sea cucumber was fermented by Corynebacterium glutamicum, the contents of crude protein, free amino acids, palmitoleic acid, linoleic acid, arachidonic acid, and the total content of polyunsaturated fatty acids were significantly increased. By feeding the fermented food, the weight gain rate, special growth rate and feed conversion rate of the sea cucumber were significantly increased, and the mortality rate was significantly reduced in the challenge test. The cellulase activity in the gut of the sea cucumber fed with the fermented feed was significantly increased, while the activities of alkaline phosphatase, acid phosphatase, total nitric oxide synthase, catalase, and lysozyme in the coelomic fluid were significantly increased. The fermented feed changed the gut microbiota of the sea cucumber and significantly reduced the relative abundance of Vibrio, which was the main pathogen causing skin ulcer syndrome. Transcriptome analysis revealed 4492 differentially expressed genes that can be enriched in biological processes such as immune system processes and immune responses, and affect the growth performance and immune regulation of the sea cucumber through metabolic pathways such as ribosomal biogenesis. Further gene expression analysis showed that the upregulation of genes such as NF kappa BI, TLR, TLR3, TRAF6, MyD88, and p38 activated the TLR signaling pathway and enhances the immune response of the sea cucumber. Therefore, C. glutamicum fermented feed can promote the growth of the sea cucumber, enhance non-specific immunity, and resist pathogen infection, making it a highly promising feed for application.