Molecular ecological network analysis reveals the effects of probiotics and florfenicol on intestinal microbiota homeostasis: An example of sea cucumber.

Animal gut harbors diverse microbes that play crucial roles in the nutrition uptake, metabolism, and the regulation of host immune responses. The intestinal microbiota homeostasis is critical for health but poorly understood. Probiotics Paracoccus marcusii DB11 and Bacillus cereus G19, and antibiotics florfenicol did not significantly impact species richness and the diversity of intestinal microbiota of sea cucumber, in comparison with those in the control group by high-throughput sequencing. Molecular ecological network analysis indicated that P. marcusii DB11 supplementation may lead to sub-module integration and the formation of a large, new sub-module, and enhance species-species interactions and connecter and module hub numbers. B. cereus G19 supplementation decreased sub-module numbers, and increased the number of species-species interactions and module hubs. Sea cucumber treated with florfenicol were shown to have only one connecter and the lowest number of operational taxonomic units (OTUs) and species-species interactions within the ecological network. These results suggested that P. marcusii DB11 or B. cereus G19 may promote intestinal microbiota homeostasis by improving modularity, enhancing species-species interactions and increasing the number of connecters and/or module hubs within the network. In contrast, the use of florfenicol can lead to homeostatic collapse through the deterioration of the ecological network.

Effects of dietary nucleotides on growth, non-specific immune response and disease resistance of sea cucumber Apostichopus japonicas.

A 9-week feeding trial was conducted to investigate the effects of dietary nucleotides (NT) on growth, immune response and disease resistance of sea cucumber Apostichopus japonicas (initial weight: 5.87 ± 0.03 g). Four graded levels of dietary NT were designed as 0, 150, 375 and 700 mg/kg, respectively. After the feeding trial, sea cucumbers were challenged with Vibrio splendidus for the determination of disease resistance. The results showed that the specific growth rates were significantly higher in sea cucumber fed the diet with 375 mg/kg NT than those fed the basal diet without NT supplementation (P < 0.05). The highest total coelomocytes counts in coelomic fluid were found in the treatment with 150 mg/kg of dietary NT (P < 0.05). Compared to those fed with the basal diet, sea cucumber fed diets with nucleotides (≥ 375 mg/kg) had significantly higher phagocytic activities in coelomic fluid (P < 0.05). Respiratory burst activities in coelomic fluid significantly increased with increasing dietary NT supplementations up to 700 mg/kg (P < 0.05). No significant differences in the activities of superoxide dismutase, total nitric oxide synthase and acid phosphatase in coelomic fluid were found among all the treatments (P > 0.05). After being challenged with V. splendidus, the cumulative mortalities of sea cucumber fed diets with 150 and 375 mg/kg NT were significantly lower than that in the treatment without dietary nucleotide supplementation (P < 0.05). Under the experimental conditions, the present results confirmed that a diet supplemented with 375 mg/kg NT is able to enhance both non-specific immune response and growth of sea cucumber in vivo. In conclusion, it was showed that dietary NT does increase the growth performance, non-specific immunity and disease resistance of sea cucumber. The optimum dietary NT supplementation level for sea cucumber was found to be 375 mg/kg. The application of dietary NT may present a novel strategy for health management in sea cucumber's aquaculture.

The effects of dietary lead on growth, bioaccumulation and antioxidant capacity in sea cucumber, Apostichopus japonicus.

Three different diets amended with lead nitrate [Pb(NO3)2] (100, 500 and 1000mg Pb/kg dry weight) and a Pb-free control diet (1.03mg Pb/kg dry weight) were fed to sea cucumber (Apostichopus japonicus) for 30 days. The patterns of Pb accumulation over time were determined in various tissues (body wall, intestine and respiratory tree), as well as growth performance and antioxidant enzymes activities. Pb accumulation in body wall and intestine increased with time in all dietary Pb treatments. When fed the highest Pb diet, the body wall exhibited the greatest Pb burden (16.37mg Pb/kg tissue wet weight), while Pb content in the intestine (2.68mg Pb/kg tissue wet weight) and the respiratory tree (1.78mg Pb/kg tissue wet weight) were lower than Pb content in the body wall by day 30. The body weight gain (BWG), specific growth rate (SGR) and survival rate (SR) had not been affected by 30 days oral administration of Pb supplemented diet. However, the antioxidant enzymes activities [superoxide dismutase (SOD) and glutathione peroxidase (GSH-Px)] of test groups were lower than control group in body wall and malondialdehyde (MDA) concentration in the body wall was opposite after 30 days in sea cucumbers. In summary, this work reports toxic effects in sea cucumber, A. japonicus, after dietary exposure to Pb.

Deposit-feeding sea cucumbers enhance mineralization and nutrient cycling in organically-enriched coastal sediments.

BACKGROUND: Bioturbators affect multiple biogeochemical interactions and have been suggested as suitable candidates to mitigate organic matter loading in marine sediments. However, predicting the effects of bioturbators at an ecosystem level can be difficult due to their complex positive and negative interactions with the microbial community. METHODOLOGY/PRINCIPAL FINDINGS: We quantified the effects of deposit-feeding sea cucumbers on benthic algal biomass (microphytobenthos, MPB), bacterial abundance, and the sediment-seawater exchange of dissolved oxygen and nutrients. The sea cucumbers increased the efflux of inorganic nitrogen (ammonium, NH(4) (+)) from organically enriched sediments, which stimulated algal productivity. Grazing by the sea cucumbers on MPB (evidenced by pheopigments), however, caused a net negative effect on primary producer biomass and total oxygen production. Further, there was an increased abundance of bacteria in sediment with sea cucumbers, suggesting facilitation. The sea cucumbers increased the ratio of oxygen consumption to production in surface sediment by shifting the microbial balance from producers to decomposers. This shift explains the increased efflux of inorganic nitrogen and concordant reduction in organic matter content in sediment with bioturbators. CONCLUSIONS/SIGNIFICANCE: Our study demonstrates the functional role and potential of sea cucumbers to ameliorate some of the adverse effects of organic matter enrichment in coastal ecosystems.

Antischistosomal effect of holothurin extracted from some Egyptian sea cucumbers.

CONTEXT: Holothuria polii (H. polii) Linnaeus (Holothuriidae), Actinopyga mauritiana (A. mauritiana) Quoy & Gaimard (Holothuriidae) and Bohadschia vitiensis (B. vitiensis) Semper (Holothuriidae) are sea cucumbers inhabiting the coasts of Egypt. Their tegument and the cuvierian gland contained a substance called holothurin that was used in traditional medicine. These three species are abundant in the Egyptian coast, however there are no reports about their efficacy as antiparasitic agent. OBJECTIVE: The antischistosomal effect of the holothurin extracted from the three species of sea cucumber is investigated. MATERIALS AND METHODS: The ethanol extract was made from the tegument of both H. polii and A. mauritiana while it was made from the cuvierian gland of B. vitiensis. The body wall (or cuvierian gland) of the sea cucumber was blended with 95% ethanol in a volume = 4 × tissue weight. Extraction was done at room temperature for one day then filtered. The ethanol was removed by evaporation using Rotavapour (BÜCHI 461 water bath REIII) at 40°C. Later the aqueous residue was placed in a vacuum oven at 20°C for about 48 h to remove water. The resulting dried mass was then stored at -4°C until use. The percentage yield and the LD50 were calculated for each extract. Each extract was administered orally to Shistosoma mansoni infected mice in acute and chronic phases of infection. The dose of one-tenth of LD50 of each extract was administrated to mice (5.4, 62.2, and 10 mg/kg body weight/mouse for H. polii extract (HPE), A. mauritiana extract (AME), and cuvierian gland of B. vitiensis, respectively) for 24 h. The effects of each extract on the worm burden and total egg count was studied. The effects of each extract on the worm tegument using scanning electron microscope (SEM) were investigated in vivo and in vitro. RESULTS: The percentage yield of cuvierian gland extract (CGE) was higher (70%) than the tegument AME (33.4%) and HPE (9.3%). The 24 h LD50 of investigated sea cucumber ethanol extracts were 54.46, 627, and 100 mg/kg body weight/mouse for HPE, AME, and CGE. Oral administration of HPE caused decrease in male and female worm burden of 30-day infected mice to reach 60 and 90%, respectively. HPE decreased the egg count significantly in those mice with 30-day (1.75 egg counts/g tissue, p < 0.05) and 45-day (3.25 egg counts/g tissue, p < 0.05) infections. SEM studies of recovered worms from treated mice with all extracts showed different tegumental changes like formation of blebs, wrinkling, formation of numerous pores, and rupturing of some tubercles. These effects were more pronounced in those worms treated in vitro represented by severe shrinkage of the tegument, deformation of spines, rupturing, and collapsing of tubercles. DISCUSSION AND CONCLUSION: Results support the hypothesis that holothurin is a promising antischistosomal agent.