Biological characteristics and pathogenicity of a highly pathogenic Shewanella marisflavi infecting sea cucumber, Apostichopus japonicus

A novel short-type peptidoglycan recognition protein with unique polysaccharide recognition specificity in sea cucumber, Apostichopus japonicus

Pattern recognition receptors (PRRs) are the first line of immune defense in invertebrates against pathogen infection; they recognize pathogens and transmit signals to downstream immune pathways. Among these, peptidoglycan recognition proteins (PGRPs) are an important family in invertebrates that generally comprise of complicated isoforms. A comprehensive understanding of PGRPs in evolutionarily and economically important marine invertebrates, such as the sea cucumber, Apostichopus japonicus, is crucial. Previous studies have identified two PGRPs in sea cucumber, AjPGRP-S and AjPGRP-S1, and another novel short-type PGRP, AjPGRP-S3, was additionally identified here. The full-length cDNA sequence of AjPGRP-S3 was obtained here by PCR-RACE, followed by which showed its gene expression analyses by in situ hybridization that showed it to be relatively highly expressed in coelomocytes and tube feet. Based on an analysis of the recombinant protein, rAjPGRP-S3, a board-spectrum pathogen recognition ability was noted that covered diverse Gram-negative and -positive bacteria, and fungi. Moreover, according to the results of yeast two-hybridization, it was suggested that rAJPGRP-S3 interacted with multiple immune-related factors, including proteins involved in the complement system, extracellular matrix, vesicle trafficking, and antioxidant system. These findings prove the important functions of AjPGRP-S3 in the transduction of pathogen signals to downstream immune effectors and help explore the functional differences in the AjPGRP isoforms.

Identification of Shewanella putrefaciens as a novel pathogen of the largemouth bass (Micropterus salmoides) and histopathological analysis of diseased fish

The largemouth bass (Micropterus salmoides) is an economically important aquaculture species in China, and its production has increased rapidly in recent years. Although Shewanella putrefaciens is known to infect several fish species, its role in infecting M. salmoides is relatively unknown. Here, we isolated a gram-negative bacterial strain (termed XX2021) from farmed largemouth bass. Based on the results of 16S rRNA sequencing and phylogenetic analyses, the isolate was identified as S. putrefaciens. The virulence of XX2021 was dependent on water temperature, such as the LD50 values were 4.21×104, 7.26×105, and 2.47×106 CFU/g fish weight at 10°C, 18°C, and 25°C, respectively. Four virulent genes—including dksA, hem, lonR, and fur—were screened through a PCR assay. The results of an antibiotic resistance test showed that XX2021 was sensitive to kanamycin, cefotaxime, doxycycline, sulfamethoxazole, florfenicol, tetracycline, and gentamicin; showed intermediate susceptibility to streptomycin, ampicillin, and norfloxacin; and was resistant to nalidixic acid and penicillin. XX2021-infected fish showed clinical symptoms typical of S. putrefaciens infection. In addition, we re-isolated XX2021 from infected fish and confirmed its identity using 16S rRNA sequencing. Histopathological changes were observed in the intestine, head kidney, spleen, and liver of diseased fish. This study presents the first report of the pathogenic effects of S. putrefaciens in farmed largemouth bass. Our findings may help develop effective disease control strategies for aquaculture fish and prevent disease outbreaks under low water temperatures.

Evaluation of Potential Probiotic Properties of a Strain of Lactobacillus plantarum for Shrimp Farming: From Beneficial Functions to Safety Assessment

In recent years the safety of probiotics has received increasing attention due to the possible transfer and spread of virulence factors (VFs) and antibiotic resistance genes (ARGs) among microorganisms. The safety of a strain of Lactobacillus plantarum named W2 was evaluated in phenotype and genotype in the present study. Its probiotic properties were also evaluated both in vivo and in vitro, including adherence properties, antibacterial properties and beneficial effects on the growth and immunity of Pacific white shrimp, Penaeus vannamei. Hemolysis tests, antibiotic resistance tests and whole genome sequence analysis showed that W2 had no significant virulence effects and did not carry high virulence factors. W2 was found to be sensitive to chloramphenicol, clindamycin, gentamicin, kanamycin and tetracycline, and to be resistant to ampicillin and erythromycin. Most ARGs have no transfer risk and a few have transfer risk but no significant enrichment in human-associated environments. The autoaggregation of W2 was 82.6% and the hydrophobicity was 81.0%. Coaggregation rate with Vibrio parahaemolyticus (24.9%) was significantly higher than Vibrio's autoaggregation rate (17.8%). This suggested that W2 had adhesion potential to mucosal/intestinal surfaces and was able to attenuate the adherence of V. parahaemolyticus. In addition, several adhesion-related protein genes, including 1 S-layer protein, 1 collagen-binding protein and 9 mucus-binding proteins were identified in the W2 genome. W2 had efficiently antagonistic activity against 7 aquatic pathogenic strains. Antagonistic components analysis indicated that active antibacterial substances might be organic acids. W2 can significantly promote the growth of shrimp when supplemented with 1 × 10¹⁰ cfu/kg live cells. Levels of 7 serological immune indicators and expression levels of 12 hepatopancreatic immune-related genes were up-regulated, and the mortality of shrimp exposed to V. parahaemolyticus was significantly reduced. Based on the above, L. plantarum W2 can be applied safely as a potential probiotic to enhance the growth performance, immunity capacity and disease resistance of P. vannamei.

Vibrio splendidus virulence to Apostichopus japonicus is mediated by hppD through glutamate metabolism and flagellum assembly

Vibrio splendidus is the main opportunistic pathogen that causes skin ulcer syndrome in Apostichopus japonicus. hppDIn the present study, mutant V. splendidus with an in-frame deletion of hppDV.s. (MTVs) was constructed. The median lethal doses of wild-type V. splendidus (WTVs) and MTVs were 5.129 × 10⁶ and 2.606 × 10¹⁰ CFU mL⁻¹, respectively. RNA-Seq was performed using WTVs and MTVs cells at different growth stages to explore the mechanisms of the pathogenesis mediated by hppDV.s. Gene Ontology analysis showed that the expression levels of 105 genes involved in amino acid metabolism and protein binding were remarkably different between MTVs and WTVs. Kyoto Encyclopedia of Genes and Genomes analysis showed that the pathways of glutamate metabolism and flagellum assembly involved in biofilm formation and swarming motility were suppressed in MTVs. Correspondingly, the swarming motility, biofilm formation and colonisation of MTVs were remarkably decreased compared with those of WTVs. The results showed that 4-hppD catalyses tyrosine into fumarate, which could enhance glutamate metabolism and ATP production; promote flagellum assembly through the TCA cycle and lead to higher swarming, biofilm formation and colonisation abilities, to contribute to the pathogenesis of V. splendidus.

Epidemiology of a SKin Ulceration Disease (SKUD) in the sea cucumber Holothuria scabra with a review on the SKUDs in Holothuroidea (Echinodermata)

Aquacultivated sea cucumbers often suffer from SKin Ulceration Diseases (SKUDs). SKUDs have been observed in six holothuroid species from nine countries. All SKUDs present a similar symptom-the skin ulceration-and can be induced by bacteria, viruses, or abiotic factors. We here provide an update on SKUDs in holothuroids and analyse the case of the SKUD observed in Holothuria scabra in Madagascar. Field observations revealed a seasonality of the disease (i.e. wintertime maximum peak). Morphological analyses of integument ulcers showed that sea cucumbers react by forming a collagen fibre plug. Metagenomic analyses revealed a higher proportion of Vibrionaceae (Gammaproteobacteria) in ulcers in comparison to the healthy integument of the same individuals. Experimental infection assays were performed with ulcer crude extracts and bacteria isolated from these extracts (e.g. Vibrio parahaemolyticus) but did not significantly induce skin ulceration. Our results suggest that the disease is not induced by a pathogen or, at the very least, that the pathogen is not found within the ulcers as the disease is not transmissible by contact. An initial cause of the SKUD in Madagascar might be the repeated and prolonged exposures to cold temperatures. Opportunistic bacteria could settle in the dermis of ulcerated individuals and promote the ulcer extension. We propose a general nomenclature for SKUDs based on the acronym of the disease, the affected sea cucumber species (e.g. Hs for Holothuria scabra), the concerned region using an ISO code 3166-2 (e.g. MG for Madagascar), the description date (e.g. 20 for the year 2020), and, when known, the inducing agent (first letter of the general taxon, b for bacteria, v for virus in currently known cases; a a if it is an abiotic inducing parameter; nothing if the inducing cause has not been precisely identified). The disease described in this work will be designated under the name SKUD Hs-MG-20.

Mechanism of the Potential Therapeutic Candidate Bacillus subtilis BSXE-1601 Against Shrimp Pathogenic Vibrios and Multifunctional Metabolites Biosynthetic Capability of the Strain as Predicted by Genome Analysis

The global shrimp industry has suffered bacterial diseases caused mainly by Vibrio species. The typical vibriosis, acute hepatopancreatic necrosis disease (AHPND), has resulted in mass mortality and devastating economic losses. Thus, therapeutic strategies are highly needed to decrease the risk of vibriosis outbreaks. Herein, we initially identified that the growth of the causative agent of AHPND, Vibrio parahaemolyticus (VP AHPND ) and other vibrios in Pacific white shrimp (Litopenaeus vannamei) was inhibited by a Bacillus subtilis strain BSXE-1601. The natural products amicoumacins A, B, and C were purified from the cell-free supernatant from the strain BSXE-1601, but only amicoumacin A was demonstrated to be responsible for this anti-Vibrio activity. Our discovery provided the first evidence that amicoumacin A was highly active against shrimp pathogens, including the representative strain VP AHPND . Furthermore, we elucidated the amicoumacin A biosynthetic gene cluster by whole genome sequencing of the B. subtilis strain BSXE-1601. In addition to amicoumacin A, the strain BSXE-1601 genome harbored other genes encoding bacillibactin, fengycin, surfactin, bacilysin, and subtilosin A, all of which have previously reported antagonistic activities against pathogenic strains. The whole-genome analysis provided unequivocal evidence in support of the huge potential of the strain BSXE-1601 to produce diverse biologically antagonistic natural products, which may facilitate further studies on the effective therapeutics for detrimental diseases in shrimp.

Use of probiotics in aquaculture of China-a review of the past decade

China is the largest aquaculture producer in the world. Antibiotics were extensively used to ensure the development of the intensive aquaculture; however, the use of antibiotics causes safety- and environment-associated problems. As an alternative strategy to antibiotics, aquatic probiotics have attracted attention. The microbial organisms used as probiotics or tested as potential probiotics in Chinese aquaculture belong to various taxonomic divisions, including Actinobacteria, Bacteroidetes, Firmicutes, Proteobacteria and yeast. Moreover, the mixture of probiotic strains and synbiotics are also widely used. Studies on the mode of action of aquatic probiotics have extended our understanding of the probiotic effects, and novel mechanisms have been discovered, such as interference of quorum sensing. However, use of probiotics in Chinese aquaculture is still at an initial stage, and there are potential risks for some probiotic applications in aquaculture. Further regulation and management are required to normalize the production and usage of aquatic probiotics. In this review, we discuss species, effects, and mode of actions of probiotics in Chinese aquaculture since 2008. Challenges and future directions for research are also discussed.

Immunomodulatory effects of chicken egg yolk antibodies (IgY) against experimental Shewanella marisflavi AP629 infections in sea cucumbers (Apostichopus japonicus)

Skin ulceration syndrome in sea cucumbers is an infectious bacterial disease with fast and high mortality. This study investigated the protection of chicken egg yolk antibodies (IgY) on skin ulcer syndrome in sea cucumbers induced by intraperitoneally injecting Shewanella marisflavi AP629. Inactivated whole S. marisflavi AP629 cells were used as an immunogen to immunize laying hens. The highest titer of the obtained specific IgY by ELISA was 1:90000. Specific IgY significantly inhibited the growth of S. marisflavi AP629 in a liquid medium, dose-dependent manner at concentrations ranging from 0.5 to 2 mg/mL. Results obtained from scanning electron microscopy and confocal laser scanning microscopy showed that specific IgY could make bacteria agglutinate and damage the cell membrane of S. marisflavi AP629, resulting in a decrease of bacterial viability. Sea cucumbers treated with 25, 5, and 1 mg/mL anti-S. marisflavi AP629 IgY could achieve survival rates of 77.5%, 50%, and 22.5% at day 12 when the infection and injection therapy were carried out at the same time, respectively. However, survival rates of sea cucumbers treated with 25 mg/mL of nonspecific IgY were only 7.5% at day 12. All sea cucumbers in the positive control group died within twelve days after bacterial inoculation. Levels of the five humoral immune factors (LYZ, ACP, NOS, SOD, CAT) released by coelomocytes were significantly increased in the specific IgY group compared to the nonspecific IgY and positive control groups within 12 h. However, the activities of LYZ, ACP, and SOD decreased rapidly at the 48 h time point in the specific IgY group, indicating that specific IgY treatment could shorten the time needed to restore balance in sea cucumber immune systems. Oral prophylaxis with egg yolk powders was that all sea cucumbers were challenged with 4.2 × 10⁶ CFU S. marisflavi AP629 by intraperitoneal injection after 60 days of feeding. Survival rates of diets containing 10%, 5%, and 1% specific egg yolk powder were 57.5%, 52.5%, and 30% by day 12, respectively, and the survival rate was 27.5% for the nonspecific group and 22.5% for the positive control group. After feeding for 60 days, enzyme activities of LZY, NOS, and SOD were all significantly enhanced in sea cucumbers fed with specific egg yolk powder when compared to the control group (p < 0.05). This study demonstrated that the phagocytic activities of coelomocytes were significantly stimulated after specific IgY treatment over that of nonspecific IgY or without IgY treatments in sea cucumbers (p < 0.05). Overall, our results revealed that anti-S. marisflavi AP629 IgY has a positive immunomodulatory effect on sea cucumbers infected with S. marisflavi AP629.

Current trends of human infections and antibiotic resistance of the genus Shewanella

Shewanella spp. are commonly known as environmental bacteria and are most frequently isolated from aquatic areas. Currently, diseases syndromes and multidrug resistance have increasingly been reported in the genus Shewanella. Some species are associated with various infections, such as skin and soft tissue infections, as well as bacteremia. Generally, these bacteria are opportunistic and mostly affect people with an impaired immune system. This genus is also a probable vehicle and progenitor of antibiotic resistance genes. In fact, several resistance genes and mobile genetic elements have been identified in some resistant species isolated from environmental or clinical settings. These genes confer resistance to different antibiotic classes, including those used in therapies such as β-lactams and quinolones, and are generally located on the chromosome. Recently, a multidrug-resistant (MDR) plasmid harboring several drug resistance genes associated with transposons and integrons has been identified in Shewanella xiamenensis. These antibiotic resistance genes can circulate in the environment and contribute to the emergence of antibiotic resistance. This review describes different aspects of Shewanella, focusing on the infections caused by this genus, as well as their role in the propagation of antibiotic resistance via mobile genetic elements.

Use of phages to control Vibrio splendidus infection in the juvenile sea cucumber Apostichopus japonicus

In the present study, we isolated 3 bacteriophages with the ability to control Vibrio splendidus, a bacterium known to cause disease in the juvenile sea cucumber. These bacteriophages were designated as vB_VspS_VS-ABTNL-1 (PVS-1), vB_VspS_VS-ABTNL-2 (PVS-2) and vB_VspS_VS-ABTNL-3 (PVS-3). The ability of the 3 phages to inhibit the growth of V. splendidus VS-ABTNL was tested in vitro using each of the 3 phages individually or in the form of a cocktail of all 3 phages in the proportion of 1:1:1. All treated cultures produced a significant (P < 0.05) inhibition of growth of V. splendidus VS-ABTNL compared with untreated V. splendidus VS-ABTNL with the cocktail being superior to any of the 3 phages used individually. The lytic capability of the 3 phages was subsequently determined with a Spot Assay Technique performed with 4 isolates of V. splendidus, 3 other Vibrio species and 2 environmental isolates. Both PVS-1 and PVS-2 were lytic to all 4 isolates of V. splendidus while PVS-3 only inhibited the growth of 3 of them. V. splendidus VS-ABTNL was more susceptible to phage PVS-2 than the other 2 phages. In an in vivo performance trial, 360 sea cucumbers (23 ± 2 g) were randomly assigned to 1 of 6 treatments. Each treatment was housed in 3 PVC tanks (38 cm × 54 cm × 80 cm) with 20 sea cucumbers per tank. Six diets were prepared including an unsupplemented control diet, antibiotic treatment diet, 3 diets containing 1 of the 3 phages individually and a diet containing a cocktail of all 3 phages. After 60 days of feeding, all sea cucumber were challenged with V. splendidus VS-ABTNL by immersion in sea water containing a bacterial concentration of 6 × 10(6) CFU/mL for 2 days. The survival rate of sea cucumbers during the next 10 days was 18% for the unsupplemented diet, 82% for the antibiotic treatment, 82% for the phage cocktail, 65% for phage PVS-1, 58% for phage PVS-2 and 50% for phage PVS-3. There were no significant differences in weight gain, ingestion rate or feed conversion among sea cucumber fed the 4 phage treatments compared with those fed the unsupplemented diet (P > 0.05). The levels of nitric oxide synthase and acid phosphatase of sea cucumbers fed phage-containing diets were significantly (P < 0.05) increased compared with those fed the control diet. However, no significant differences (P > 0.05) were detected among the 4 phage-fed treatments. An additional study was conducted in which 60 healthy sea cucumbers (23 ± 2 g) were randomly assigned to a control, an untreated group and a test group to investigate the effects of injecting phages by coelomic injection on the survival rate and enzyme activities in the coelomic fluid of the sea cucumbers. The control was injected with 1 ml of sterilized seawater while the untreated group and the test group were injected with the same volume of V. splendidus-ABTNL culture (3 × 10(5) CFU/mL). Then, the test group was injected with 1 ml of the 3 phage cocktail (MOI = 10). After 48 h, the activities of lysozyme, acid phosphatase and superoxide dismutase were elevated in the untreated group while the levels of these enzymes in the test group were similar to the blank control. After 10-day observation, the survival rate of the sea cucumber was 100% for the blank control, 80% for the test group and 20% for the negative control. The overall results of this experiment indicate that phage therapy increased the survival of sea cucumber infected with V. splendidus VS-ABTNL. The above results demonstrate that using phages, especially a combination of different phages, may be a feasible way to control Vibrio infection in the sea cucumber industry.

Cathepsin L of the sea cucumber Apostichopus japonicus-molecular characterization and transcriptional response to Vibrio splendidus infection

Cathepsin L, a lysosomal endopeptidase, has been noted for its involvement in the innate immune response in invertebrates. Here, the cathepsin L cDNA of the sea cucumber Apostichopus japonicus (AjCatL) is identified from an EST library and then cloned by the rapid amplification of the cDNA ends (RACE) PCR. The full-length cDNA is 1678 bp long containing an open reading frame (ORF) of 1002 bp, an 80 bp 5' UTR and a 599 bp 3' UTR. The cDNA encodes 333 amino acid residues with a predicted molecular mass of 37.07 kDa and a theoretical isoelectric point (pI) of 5.01. The full-length AjCatL contains three active sites of eukaryotic thiol (cysteine) protease at positions 133-144, 278-288 and 295-314. Analysis of the predicted tertiary structure of prepro-CatL (17-333 aa) and mature-CatL (116-333 aa) reveals that the propeptide region (17-115 aa) blocks access to the substrate-binding cleft. Phylogenetic analysis shows that the AjCatL is clustered together with two other CatLs from Strongylocentrotus purpuratus. The enzymatic activity of AjCatL was verified using a substrate hydrolyzing assay with recombinant mAjCatL. Further analysis of real time-PCR demonstrates that the expression of AjCatL mRNA is significantly up-regulated in the coelomocytes in cases of infection with the common bacterial pathogen, Vibrio splendidus. This suggests that the AjCatL is likely to be involved in the immune response.

Beneficial Effects of Rhodotorula sp. C11 on Growth and Disease Resistance of Juvenile Japanese Spiky Sea Cucumber Apostichopus japonicus

The purpose of this study was to evaluate the effects of dietary administration of the live yeast, Rhodotorula sp. C11, on growth and disease resistance against Vibrio splendidus infection in juvenile Japanese spiky sea cucumber Apostichopus japonicus. Sea cucumbers were fed diets containing Rhodotorula sp. C11 at 0 (control), 10⁴, 10⁵, and 10⁶ CFU/g of feed for 45 d. There were three replicate tanks per dietary treatment. The specific growth rates were higher in all sea cucumbers treated with Rhodotorula sp. C11 than in the controls. Following a challenge with V. splendidus NB13, the cumulative prevalence and mortality of sea cucumbers fed diets supplemented with Rhodotorula sp. C11 were lower than in animals fed the basal diet. In sea cucumbers fed diets supplemented with Rhodotorula sp. C11 for 42 d, the only viable yeast found in the intestine was Rhodotorula sp. C11, which had counts of 1.58-1.98 × 10⁴CFU/g. No yeast was isolated from the intestine of animals fed the basal diet. For the colonization study, 20 sea cucumbers from each dietary treatment were removed to separate tanks and fed the control diet from day 16 to day 46. The viable yeast (Rhodotorula sp. C11) counts in the intestine decreased to 60-80 CFU/g by day 37. Moreover, as demonstrated by denaturing gradient gel electrophoresis, Rhodotorula sp. C11 colonization of the intestine could be detected until day 46. The differences in culture and PCR-denaturing gradient gel electrophoresis may be due to differences in the sensitivity of both methods. The present result showed that Rhodotorula sp. C11 was able to successfully colonize the intestine of juvenile Japanese spiky sea cucumbers by dietary supplementation, which improved its growth and disease resistance.

Distinct roles of major peptidoglycan recycling enzymes in β-Lactamase production in Shewanella oneidensis

β-Lactam antibiotics were the earliest discovered and are the most widely used group of antibiotics that work by inactivating penicillin-binding proteins to inhibit peptidoglycan biosynthesis. As one of the most efficient defense strategies, many bacteria produce β-lactam-degrading enzymes, β-lactamases, whose biochemical functions and regulation have been extensively studied. A signal transduction pathway for β-lactamase induction by β-lactam antibiotics, consisting of the major peptidoglycan recycling enzymes and the LysR-type transcriptional regulator, AmpR, has been recently unveiled in some bacteria. Because inactivation of some of these proteins, especially the permease AmpG and the β-hexosaminidase NagZ, results in substantially elevated susceptibility to the antibiotics, these have been recognized as potential therapeutic targets. Here, we show a contrasting scenario in Shewanella oneidensis, in which the homologue of AmpR is absent. Loss of AmpG or NagZ enhances β-lactam resistance drastically, whereas other identified major peptidoglycan recycling enzymes are dispensable. Moreover, our data indicate that there exists a parallel signal transduction pathway for β-lactamase induction, which is independent of either AmpG or NagZ.

Cloning and gene expression of allograft inflammatory factor-1 (AIF-1) provide new insights into injury and bacteria response of the sea cucumber Apostichopus japonicus (Selenka, 1867)

Allograft inflammatory factor-1 (AIF-1) is an interferon (IFN)-γ-inducible Ca(2+)-binding cytokine that associates with the immune defense and inflammatory response. In this study, we reported AIF-1 gene in sea cucumber Apostichopus japonicus (AjAIF-1). The full-length cDNA of AjAIF-1 is 1541 bp with an open reading frame (ORF) of 477 bp encoding 158 amino acids. Two EF-hand Ca(2+)-binding motifs were found in the deduced AjAIF-1. AjAIF-1 was widely expressed in all tested tissues (body wall, intestine, respiratory tree, tube feet, coelomocytes and longitudinal muscle), with the highest expression in respiratory tree. After Vibrio splendidus challenge and physical injury, AjAIF-1 transcripts were significantly upregulated in coelomocytes. The mRNA expression level of AjAIF-1 in coelomocytes reached to the highest value at 4 h (3.38-folds vs. the PBS control, P < 0.05) post injection. After papilla injury, the mRNA level of AjAIF-1 in coelomocytes was upregulated, and its peak value was found at 4 h (3.88-folds vs. the control, P < 0.05). These results indicated that 1) AjAIF-1 sensitively responds to pathogen infection; 2) AjAIF-1 is involved in acute inflammatory response. Our findings gain general information about the role of AjAIF-1 in the innate immunity of A. japonicus.

Identification and expression analysis of two Toll-like receptor genes from sea cucumber (Apostichopus japonicus)

Toll-like receptors (TLRs) are a family of type I integral membrane glycoproteins which play pivotal roles in innate immunity. In this study, two TLRs named AjTLR3 and AjToll were cloned from sea cucumber (Apostichopus japonicus). The full-length cDNA sequences of AjTLR3 and AjToll are 3484 bp and 4211 bp, with an open reading frame (ORF) of 2679 bp and 2853 bp, encoding 892 and 950 amino acids, respectively. Both AjTLR3 and AjToll are composed of a leucine-rich repeat (LRR) domain, a transmembrane (TM) domain and an intracellular Toll/interleukin-1 receptor (TIR) domain. Evolution analysis revealed that AjTLR3 and AjToll were clustered with the vertebrate-like TLRs (V-TLRs) and the protostome-like TLRs (P-TLRs), respectively. These two genes were widely expressed in all five tested tissues (body wall, coelomocytes, tube feet, intestine and respiratory tree), but showed different expression patterns. The significantly up-regulated expressions of AjTLR3 and AjToll after peptidoglycan (PGN), lipopolysaccharides (LPS), Zymosan A and polyinosinic-polycytidylic acid (PolyI:C) challenges suggested that they were functionally involved in the immune responses to the Cram-positive bacteria, Gram-negative bacteria, fungi and double-stranded RNA (dsRNA) viruses, respectively.

Effects of dietary live yeast Hanseniaspora opuntiae C21 on the immune and disease resistance against Vibrio splendidus infection in juvenile sea cucumber Apostichopus japonicus

A feeding experiment was conducted to determine effects of Hanseniaspora opuntiae C21 on immune response and disease resistance against Vibrio splendidus infection in juvenile sea cucumbers Apostichopus japonicus. Sea cucumbers were fed with either diets containing C21 at 10(4), 10(5) and 10(6) CFU g(-1) feed or a control diet for 30-50 days, respectively. After feeding for 30 days and 45 days, five sea cucumbers from each tank were sampled for immunological analyses. Results indicated that C21 significantly improved the phagocytic activity in coelomocytes of sea cucumbers (P < 0.05). Moreover, C21 administration significantly enhanced lysozyme (LSZ), phenoloxidase activity (PO), total nitric oxide synthase (T-NOS), superoxide dismutase (SOD), alkaline phosphatase (AKP) and acid phosphatase (ACP) activities in coelomic fluid, and LSZ, T-NOS, AKP and ACP activities in coelomocytes lysate supernatant (CLS) of sea cucumbers (P < 0.05). After feeding for 45 days, 10 sea cucumbers from each dose group were challenged with V. splendidus NB13. Cumulative incidence and mortality of sea cucumbers fed with C21 were found to be lower than those of control group. After feeding for 50 days, sea cucumbers in 10(4) CFU g(-1) C21 treatment and control tanks were subjected to acute salinity changes (from 30 to 20) for 24 h in the laboratory, and the immunological parameters were measured to evaluate the immune capacities of the A. japonicus. Phagocytic, LAZ and T-NOS activities of C21-treated group were higher than those of control group, indicating that salinity stress tolerance of sea cucumber was enhanced by C21. The present results showed that a diet supplemented with C21 could stimulate the immune system of juvenile A. japonicus thus enhancing their resistance against V. splendidus.