Dietary Cordyceps militaris protects against Vibrio splendidus infection in sea cucumber Apostichopus japonicus

Effects of dietary Vibrio sp. 33 on growth, innate immunity, gut microbiota profile and disease resistance against Vibrio splendidus of juvenile sea cucumber Apostichopus japonicus

To investigate the ability of Vibrio sp. V33 supplementation on the growth performance, innate immunity, intestinal microbiota, and disease resistance of the juvenile sea cucumber Apostichopus japonicus, a feeding experiment was conducted. Our results revealed that dietary Vibrio sp. V33 could significantly enhanced sea cucumber growth rate, and the immune parameters including total coelomocytes counts (TCC), phagocytosis, respiratory burst, immune-related enzyme activities (acid phosphatase, alkaline phosphatase, superoxide dismutase, catalase, superoxide dismutase, and nitric oxide synthetase) were all markedly improved in coelomocytes of sea cucumbers fed with V33 (P < 0.05). Furthermore, the composition of the bacterial community in the intestinal contents of the sea cucumber was surveyed by 16S rRNA sequencing. Beta diversity analysis indicated that the bacterial compositions of sea cucumbers were significantly different between V33 and Control groups. At the phylum level, Proteobacteria, Actinobacteria, Firmicutes, and Bacteroidetes were the most prevalent phyla in sea cucumber gut microbiota. The abundance of Firmicutes (20.58%), Bacteroidetes (9.77%), and Verrucomicrobia (3.04%) were significantly higher in V33 group when compared with Control. Moreover, genus Mycobacterium was markedly decreased to 0.5% after V33 feeding, while the abundance of genus Rhodococcus was significantly increased by 6.9-fold (P < 0.01) under the same condition, indicating V33 diet might promotes the colonization of beneficial bacteria in the gut of sea cucumber. After Vibrio splendidus challenge, the survival rate of juvenile sea cucumbers fed with V33 diet was significantly higher than that fed with Control diet. All our current results suggested that the Vibrio sp. V33 could used as a probiotic for healthier production of sea cucumbers in aquaculture.

A novel approach in valorization of spent mushroom substrate of Cordyceps militaris as in-feed antibiotics in Labeo rohita against Aeromonas hydrophila infection

The study was carried out to investigate Cordyceps militaris spent mushroom substrate (CMSMS), a renewable biomass, for its effect on fish as an alternative source of in-feed antibiotics. For meticulous examination, four different iso-nitrogenous and iso-caloric diets were prepared containing CMSMS at 0%, 1%, 2%, and 3%. A total of 360 Labeo rohita fingerlings with an average initial weight and length of 12.6 ± 0.04g and 10 ± 0.1 cm, respectively, were blocked into 4 treatments with 3 replicates, i.e., T1 (control), T2 (10 g/kg), T3 (20 g/kg), and T4 (30 g/kg). The feeding trial was conducted for 60 days with samplings on the 7th, 15th, 30th, and 60th days, and blood samples were collected to determine different immunological (NBT, TIg, lysozyme, and antiprotease activity) and biochemical (glucose, total protein, SGPT) parameters. A challenge study was conducted against Aeromonas hydrophila at the end of the feeding trial. The results showed that CMSMS at 30g/kg showed a better immune response over time with increasing doses. All the biochemical readings fall within normal ranges. Fish fed with CMSMS at 30g/kg (3%) have better survival after being challenged with Aeromonas hydrophila. Therefore, Cordyceps militaris spent mushroom substrate (CMSMS) can be biosafely used as in-feed antibiotics in Labeo rohita and can reduce the concern of by-product disposal from mushroom cultivation.

Exogenous c-di-GMP inhibited the biofilm formation of Vibrio splendidus

Vibrio splendidus, a gram-negative bacterium that is ubiquitously present in marine environments, has been increasingly deemed an important opportunistic pathogen of marine animals. In this study, the biofilm formation of V. splendidus was quantitatively determined and morphologically characterized. Three stages of biofilm formation, including adhesion, aggregation and maturation were observed in the biofilm formed by V. splendidus. The inhibitory effect of exogenous bis (3',5')-cyclic dimeric guanosine monophosphate (c-di-GMP) on the biofilm formation from the scratch and preformed established biofilms of V. splendidus was determined. When 200 μmol/L c-di-GMP was added, the quantity of biofilm decreased by 88.1% or 66.7% under the two conditions. To explore the preliminary mechanism of exogenous c-di-GMP on the biofilm formed by V. splendidus, proteomic analysis was performed. GO enrichment analysis showed that exogenous c-di-GMP upregulated biological processes, including the tricarboxylic acid cycle, oxidation‒reduction reactions and organonitrogen compound catabolism and significantly downregulated tRNA threonylcarbamoyladenosine modification, protein dephosphorylation, and lactate transmembrane transporter activity. Sequence-specific DNA binding activity was the most markedly downregulated molecular function. KEGG analysis showed that the valine, leucine and isoleucine degradation pathway was the most enriched pathway, followed by nitrogen metabolism, among the 20 upregulated pathways. Among the downregulated pathways, a nonribosomal peptide structure pathway and the streptomycine, polyketide sugar unit, acarbose and validamycin biosynthesis pathways were significantly enriched. Our present study provides basic data for the biofilm formation of V. splendidus and the preliminary inhibitory mechanism of exogenous c-di-GMP on the biofilm formation of V. splendidus.

Effects of microbial community and disease resistance against Vibrio splendidus of Yesso scallop (Patinopecten yessoensis) fed supplementary diets of tussah immunoreactive substances and antimicrobial peptides

This study was conducted to investigate the effects of dietary supplementation of tussah immunoreactive substances (TIS) and antimicrobial peptides (AMPs) on microbial community and resistance against Vibrio splendidus of Yesso scallop Patinopecten yessoensis. Scallops were fed with the basal diets supplemented with TIS (T group), AMPs (A group), or both of the two (TA group). After the feeding trial, the microbial community changes were evaluated, and the challenge test with V. splendidus was conducted, as well as the immune parameters and digestive enzyme activities were determined. The results revealed that the TA group was more capable of modulating the bacterial community composition of scallops by increasing the potentially beneficial bacteria and suppressing the pathogenic microorganism during the feeding trial. After injection, the cumulative mortality rate in TA group was notably lower than others. In addition, the TA group showed better digestive and immune parameters involved in digestive capacity, phagocyte function, phosphatase-responsiveness, and oxidation resistance. These results collectively confirmed that dietary TIS and AMPs in diet could effectively modulate the microflora structure and improve disease resistance against V. splendidus of scallop, and the positive effects were more obvious when dietary supplementation of them in combination.

A novel fucolectin from Apostichopus japonicus with broad PAMP recognition pattern

F-type lectin (also known as fucolectin) is a newly identified family of fucose binding lectins with the sequence characters of a fucose binding motif and a unique lectin fold (the "F-type" fold). In the present study, a fucolectin was identified from sea cucumber Apostichopus japonicus (designated AjFL-1). The open reading frame (ORF) of AjFL-1 was of 546 bp, encoding a polypeptide of 181 amino acids with a predicted molecular mass of about 20 kDa. The deduced amino acid sequence of AjFL-1 shared 30%-40% similarity with the fucolectins from other animals. There were a typical F-type lectin domain (FLD) (residues 39-180) and a signal peptide (residues 1-24) in AjFL-1. The mRNA transcript of AjFL-1 could be detected by qRT-PCR in various tissues, such as intestinum, coelomocytes, respiratory tree, tentacle, and body wall, while undetectable in the gonads and longitudinal muscle. The mRNA expression level of AjFL-1 in coelomocytes was significantly up-regulated (47.06-fold to that in control group, p < 0.05) at 12 h after Vibrio splendidus challenge. Immunofluorescence assay showed that AjFL-1 protein was mainly distributed on the membrane, while few in cytoplasm of coelomocytes in sea cucumber. The recombinant AjFL-1 (rAjFL-1) could bind lipopolysaccharide (LPS), peptidoglycan (PGN), mannan (MAN) and fucose (FUC), and exhibited a broader binding activities towards Gram-negative bacterium Escherichia coli, Gram-positive bacterium Micrococcus luteus, as well fungus Pichia pastoris. In addition, rAjFL-1 could strongly promote the agglutination of fungus P. pastoris. These results indicated that AjFL-1 was a novel member of fucose-binding lectin family, which functioned as a pattern recognition receptor with broad spectrum of microbial recognition, and involved in innate immune response of sea cucumber.

Immune-related proteins detected through iTRAQ-based proteomics analysis of intestines from Apostichopus japonicus in response to tussah immunoreactive substances

Apostichopus japonicus is a species of sea cucumber that is extensively bred as a marine delicacy because of its high nutritive and medicinal value. Immunostimulants are usually used to enhance the immunity of sea cucumber against diseases, but the physiological function of immunostimulants is poorly understood. In this study, we fed A. japonicus individuals with a diet supplemented with different concentrations of tussah immunoreactive substances (TIS), and then subjected their intestines to iTRAQ-based proteomic analysis. A total of 51 differentially expressed proteins were detected in response to TIS, 13 proteins were upregulated, while 38 proteins were reduced. These proteins are involved in phagocytosis, tissue protection, cell apoptosis and energy metabolism. Among these 51 proteins, 7 proteins (GLO2, ACOX, CTTN, MARK, FADD, CSTA and CASP6) related to immunity with functional annotation in sea cucumber were further analyzed. In addition, the upregulated expression of 4 immune-related proteins (GLO2, ACOX, CTTN and MARK) was validated by qRT-PCR. The findings of this study gave further insight into the mechanism by which TIS might enhance the immunity of A. japonicus.

Effects of tussah immunoreactive substances on growth, immunity, disease resistance against Vibrio splendidus and gut microbiota profile of Apostichopus japonicus

Tussah immunoreactive substance (TIS) comprises a number of active chemicals with various bioactivities. The current study investigated the effects of these substances on the sea cucumber Apostichopus japonicus. The specific growth rate (SGR) of TIS-fed sea cucumbers was significantly enhanced, whereas no significant difference in SGR was observed between those soaked in antibiotics and those fed with basal diet only. TIS also improved the immune response of the animals when given at a dose of 1.0% or 2.0%, as shown by increased phagocytic, lysozyme, superoxide dismutase, alkaline phosphatase, acid phosphatase, and catalase activities following injection with live Vibrio splendidus. At a dose of 1.0% or 2.0%, TIS significantly enhanced the immune ability (P < 0.05) of the sea cucumbers, but except for lysozyme activity, other immune indices were reduced one day after the animals were injected with Vibrio splendidus. However, the values of these immune indexes were still significantly higher compared to those of the control groups (P < 0.05). Intestinal micro flora counts and high-throughput sequencing showed that dietary TIS could improve the amount of probiotic bacteria, yielding a 6-fold increase in Bacillus and 10-fold increase in Lactobacillus for sea cucumbers fed with 2.0% TIS diet compared to the control. Furthermore, TIS-containing diet also greatly reduced the number of harmful bacteria, with the number of Vibrio in sea cucumbers fed with 1%TIS diet decreased by 67% compared to the control. The results thus indicated that TIS increased the growth of sea cucumbers and enhanced their resistance to V. splendidus infection by improving the immunity of the animals. TIS also improved the gut microbiota profiles of the animals by increasing the probiotics and reducing the harmful bacteria within their guts.

Identification and functional characterization of TNF receptor associated factor 3 in the sea cucumber Apostichopus japonicus

TNF receptor associated factors (TRAFs) are a family of proteins primarily involved in both adaptive and innate immunity. In this study, we identified a novel TRAF3 gene in Apostichopus japonicus by transcriptome sequencing and RACE approaches (designated as AjTRAF3). The full-length of AjTRAF3 was of 2796 bp including a 5' untranslated region (UTR) of 83 bp, a 3' UTR of 1066 bp and a putative open reading frame of 1647 bp encoding a polypeptide of 548 amino acid residues. The representative domains such as a RING finger domain (residues 54-96), two TRAF domains with zinc finger structure (residues 141-228), a coiled coil and a meprin and TRAF homology (MATH) domain (residues 396-522) were all detected in the deduced amino acids of AjTRAF3. AjTRAF3 was ubiquitously expressed in all examined tissues with predominant expression in the body wall and slightly weaker in intestine, respiratory tree, tube feet, coelomocytes and longitudinal muscle. Time-course expression analysis in coelomocytes revealed that AjTRAF3 was significantly depressed towards Vibrio splendidus infection with a 0.20-fold decrease at 12 h, compared to control levels. AjTRAF3 silencing could elevate intracellular ROS levels by 2.08-fold and 2.09-fold compared to each control group in vitro and in vivo, respectively. Taken together, all these results suggested that AjTRAF3 may play a crucial role in the processes of anti-bacteria response in sea cucumber through regulating ROS production.