Morphologic, cytometric, quantitative transcriptomic and functional characterisation provide insights into the haemocyte immune responses of Pacific abalone (Haliotis discus hannai)

In recent years, the abalone aquaculture industry has been threatened by the bacterial pathogens. The immune responses mechanisms underlying the phagocytosis of haemocytes remain unclear in Haliotis discus hannai. It is necessary to investigate the immune mechanism in response to these bacterial pathogens challenges. In this study, the phagocytic activities of haemocytes in H. discus hannai were examined by flow cytometry combined with electron microscopy and transcriptomic analyses. The results of Vibrio parahaemolyticus, Vibrio alginolyticus and Staphylococcus aureu challenge using electron microscopy showed a process during phagosome formation in haemocytes. The phagocytic rate (PP) of S. aureus was higher than the other five foreign particles, which was about 63%. The PP of Vibrio harveyi was about 43%, the PP peak of V. alginolyticus in haemocyte was 63.7% at 1.5 h. After V. parahaemolyticus and V. alginolyticus challenge, acid phosphatase, alkaline phosphatase, total superoxide dismutase, lysozyme, total antioxidant capacity, catalase, nitric oxide synthase and glutathione peroxidase activities in haemocytes were measured at different times, differentially expressed genes (DEGs) were identified by quantitative transcriptomic analysis. The identified DEGs after V. parahaemolyticus challenge included haemagglutinin/amebocyte aggregation factor-like, supervillin-like isoform X4, calmodulin-like and kyphoscoliosis peptidase-like; the identified DEGs after V. alginolyticus challenge included interleukin-6 receptor subunit beta-like, protein turtle homolog B-like, rho GTPase-activating protein 6-like isoform X2, leukocyte surface antigen CD53-like, calponin-1-like, calmodulin-like, troponin C, troponin I-like isoform X4, troponin T-like isoform X18, tumor necrosis factor ligand superfamily member 10-like, rho-related protein racA-like and haemagglutinin/amebocyte aggregation factor-like. Some immune-related KEGG pathways were significantly up-regulated or down-regulated after challenge, including thyroid hormone synthesis, Th17 cell differentiation signalling pathway, focal adhesion, melanogenesis, leukocyte transendothelial migration, inflammatory mediator regulation of TRP channels, ras signalling pathway, rap1 signalling pathway. This study is the first step towards understanding the H. discus hannai immune system by adapting several tools to gastropods and providing a first detailed morpho-functional study of their haemocytes.

Identification, diversity, and evolution analysis of Commd gene family in Haliotis discus hannai and immune response to biotic and abiotic stresses

The Commd (Copper Metabolism gene MURR1 Domain) family genes play crucial roles in various biological processes, including copper and sodium transport regulation, NF-κB activity, and cell cycle progression. Their function in Haliotis discus hannai, however, remains unclear. This study focused on identifying and analyzing the Commd genes in H. discus hannai, including their gene structure, phylogenetic relationships, expression profiles, sequence diversity, and alternative splicing. The results revealed significant homology between H. discus hannai's Commd genes and those of other mollusks. Both transcriptome quantitative analysis and qRT-PCR demonstrated the responsiveness of these genes to heat stress and Vibrio parahaemolyticus infection. Notably, alternative splicing analysis revealed that COMMD2, COMMD4, COMMD5, and COMMD7 produce multiple alternative splice variants. Furthermore, sequence diversity analysis uncovered numerous missense mutations, specifically 9 in COMMD5 and 14 in COMMD10. These findings contribute to expanding knowledge on the function and evolution of the Commd gene family and underscore the potential role of COMMD in the innate immune response of H. discus hannai. This research, therefore, offers a novel perspective on the molecular mechanisms underpinning the involvement of Commd genes in innate immunity, paving the way for further explorations in this field.

Comparative Responses of Orange-Foot and Common-Foot Haliotis gigantea to Carotenoid-Enriched Diets: Survival, Heat Tolerance, and Bacterial Resistance

Carotenoids, known to enhance survival, heat tolerance, and bacterial resistance, play an essential role in the nutrition of economically important aquatic animals. This study specifically examined their impact as feed additives on the abalone Haliotis gigantea. We prepared 13 compound feeds with varying levels of astaxanthin, zeaxanthin, and β-carotene, and administered them to both common-footed and orange-footed H. gigantea. The survival rate of H. gigantea was about 70-80%, with no significant differences in survival observed among the various carotenoid-supplemented feeding groups or when compared with the control group, nor between orange-footed and common-footed individuals. In heat attachment duration experiments, orange-foot abalones exhibited longer attachment durations with certain concentrations of astaxanthin and zeaxanthin, whereas common-foot abalones showed extended durations with astaxanthin, zeaxanthin, and β-carotene, indicating that common-foot abalones might benefit more from these carotenoids. Additionally, our results showed similar patterns and levels of Vibrio harveyi AP37 resistance in both orange-footed and common-footed H. gigantea, suggesting a uniform response to carotenoid supplementation in their bacterial defense mechanisms. This study suggests the potential benefits of carotenoid supplementation in H. gigantea and contributes to the theoretical basis for developing high-quality artificial compound feeds.

Cold temperature stress and damaged skin induced high mortality in barramundi (Lates calcarifer) challenged with Vibrio harveyi

Most diseases in aquaculture are caused by opportunistic pathogens. One of them, Vibrio harveyi, is a widespread Gram-negative bacterium that has become an important pathogen of aquatic species in marine environments. Here, we propose the use of the causal pie model as a framework to conceptualize the causation of vibriosis in juvenile barramundi (Lates calcarifer) and to establish an effective challenge model. In the model, a sufficient cause, or the causal pie, is a constellation of component causes that lead to an outcome (e.g. vibriosis). In the pilot study, a high cumulative mortality (63.3% ± 10.0%, mean ± SE) was observed when V. harveyi was administered by intraperitoneal injection using a high challenge dose [10⁷ colony-forming units (CFU) fish^-1 ], but low or no mortality was observed in fish subject to cold stress or fish with intact skin when challenged by immersion. We, therefore, tested the use of a skin lesion (induced with a 4-mm biopsy punch) combined with cold temperature stress to induce vibriosis following the causal pie model. After challenge, fish were immediately subject to cold stress (22°C) or placed at an optimal temperature of 30°C. All groups were challenged with 10⁸  CFU mL^-1 for 60 min. A considerably higher mortality level (72.7% ± 13.9%) was observed in fish challenged with both a skin lesion and cold stress compared with mortality in fish only having a skin lesion (14.6% ± 2.8%). V. harveyi was re-isolated from all moribund fish and was detected by species-specific real-time PCR in gills, head kidney and liver, regardless of challenge treatment confirming vibriosis as the cause of disease. Parenchymal tissues had histopathological changes consistent with vibriosis. Whole-genome sequence (WGS) is provided for the Vibrio harveyi isolate examined in this study. Overall, the causal pie model was a useful framework to conceptualize the design of the experimental challenge model, in which both cold stress and skin damage were identified as component causes of vibriosis with high mortality. This conceptual framework can be applied to other opportunistic pathogens in aquaculture or to the study of co-infections in fish.

Molecular mechanisms underlying the vulnerability of Pacific abalone (Haliotis discus hannai) to Vibrio harveyi infection at higher water temperature

Climate change is one of the most important threats to farmed abalone worldwide. Although abalone is more susceptible to vibriosis at higher water temperatures, the molecular mode of action underlying this has not been fully elucidated. Therefore, this study aimed to address the high susceptibility of Halitotis discus hannai to V. harveyi infection using abalone hemocytes exposed to low and high temperatures. Abalone hemocytes were divided into four groups, 20C, 20V, 25C, and 25V, depending on co-culture with (V)/without (C) V. harveyi (MOI = 12.8) and incubation temperature (20 °C or 25 °C). After 3 h of incubation, hemocyte viability and phagocytic activity were measured, and RNA sequencing was performed using Illumina Novaseq. The expression of several virulence-related genes in V. harveyi was analyzed using real-time PCR. The viability of hemocytes was significantly decreased in the 25V group compared to cells in the other groups, whereas phagocytic activity at 25 °C was significantly higher than at 20 °C. Although a number of immune-associated genes were commonly upregulated in abalone hemocyte exposed to V. harveyi, regardless of temperature, pathways and genes regarding pro-inflammatory responses (interleukin-17 and tumor necrosis factor) and apoptosis were significantly overexpressed in the 25V group compared to the 25C group. Notably, in the apoptosis pathway, genes encoding executor caspases (casp3 and casp7) and pro-apoptotic factor, bax were significantly up-regulated only in the 25V group, while the apoptosis inhibitor, bcl2L1 was significantly up-regulated only in the 20V group compared to the control group at the respective temperatures. The co-culture of V. harveyi with abalone hemocytes at 25 °C up-regulated several virulence-related genes involved in quorum sensing (luxS), antioxidant activity (katA, katB, and sodC), motility (flgI), and adherence/invasion (ompU) compared to those at 20 °C. Therefore, our results showed that H. discus hannai hemocytes exposed to V. harveyi at 25 °C were highly stressed by vigorously activated inflammatory responses and that the bacterial pathogen overexpressed several virulence-related genes at the high temperature tested. The transcriptomic profile of both abalone hemocytes and V. harveyi in the present study provide insight into differential host-pathogen interactions depending on the temperature conditions and the molecular backgrounds related to increased abalone vulnerability upon global warming.

Isolation and Characterization of a Novel Vibrio natriegens—Infecting Phage and Its Potential Therapeutic Application in Abalone Aquaculture

Phage-based pathogen control (i.e., phage therapy) has received increasing scientific attention to reduce and prevent the emergence, transmission, and detrimental effects of antibiotic resistance. In the current study, multidrug-resistant Vibrio natriegens strain AbY-1805 was isolated and tentatively identified as a pathogen causing the death of juvenile Pacific abalones (Haliotis discus hannai Ino). In order to apply phage therapy, instead of antibiotics, to treat and control V. natriegens infections in marine aquaculture environments, a lytic phage, vB_VnaS-L3, was isolated. It could effectively infect V. natriegens AbY-1805 with a short latent period (40 min) and high burst size (~890 PFU/cell). Treatment with vB_VnaS-L3 significantly reduced the mortality of juvenile abalones and maintained abalone feeding capacity over a 40-day V. natriegens challenge experiment. Comparative genomic and phylogenetic analyses suggested that vB_VnaS-L3 was a novel marine Siphoviridae-family phage. Furthermore, vB_VnaS-L3 had a narrow host range, possibly specific to the pathogenic V. natriegens strains. It also exhibited viability at a wide range of pH, temperature, and salinity. The short latent period, large burst size, high host specificity, and broad environmental adaptation suggest that phage vB_VnaS-L3 could potentially be developed as an alternative antimicrobial for the control and prevention of marine animal infections caused by pathogenic V. natriegens.

Susceptibility of Four Abalone Species, Haliotis gigantea, Haliotis discus discus, Haliotis discus hannai and Haliotis diversicolor, to Abalone asfa-like Virus

Abalone amyotrophia is a viral disease that causes mass mortality of juvenile Haliotis discus and H. madaka. Although the cause of this disease has yet to be identified, we had previously postulated a novel virus with partial genome sequence similarity to that of African swine fever virus is the causative agent and proposed abalone asfa-like virus (AbALV) as a provisional name. In this study, three species of juvenile abalone (H. gigantea, H. discus discus, and H. diversicolor) and four species of adult abalone (the above three species plus H. discus hannai) were experimentally infected, and their susceptibility to AbALV was investigated by recording mortality, quantitatively determining viral load by PCR, and conducting immunohistological studies. In the infection test using 7-month-old animals, H. gigantea, which was previously reported to be insusceptible to the disease, showed multiplication of the virus to the same extent as in H. discus discus, resulting in mass mortality. H. discus discus at 7 months old showed abnormal cell masses, notches in the edge of the shell and brown pigmentation inside of the shell, which are histopathological and external features of this disease, while H. gigantea did not show any of these characteristics despite suffering high mortality. Adult abalones had low mortality and viral replication in all species; however, all three species, except H. diversicolor, became carriers of the virus. In immunohistological observations, cells positive for viral antigens were detected predominantly in the gills of juvenile H. discus discus and H. gigantea, and mass mortality was observed in these species. In H. diversicolor, neither juvenile nor adult mortality from infection occurred, and the AbALV genome was not increased by experimental infection through cohabitation or injection. Our results suggest that H. gigantea, H. discus discus and H. discus hannai are susceptible to AbALV, while H. diversicolor is not. These results confirmed that AbALV is the etiological agent of abalone amyotrophia.

Influence of intensive net cage farming on hydrodynamic and geochemical environmental conditions and the mass mortality of abalone in South Korea

The abalone aquaculture industry in South Korea has grown rapidly since the 2000s. In this study, we investigated the sedimentary pollution at four major abalone farms responsible for ~60% of all South Korean abalone produced. We also surveyed the current statuses of cage facilities, abalone mass mortality, and current velocities within and outside farm cages. The concentrations of total organic carbon in the study area were 7.92 ± 2.09 mg g^-1, indicating a mild level of sedimentary pollution. We observed higher mortality rates in rectangular-shaped shelter cages than in triangular shelters. With increases in the number and size of abalone farming facilities, current velocities inside the cages declined by an average of 45% relative to those outside the cages, leading to poor habitat conditions for farmed abalone. Our results provide insights into the current status of the benthic environments and major causes of mass mortality in the abalone farms of South Korea.

Immune response in probiotic-fed New Zealand black-footed abalone (Haliotis iris) under Vibrio splendidus challenge

Vibriosis disease is a major constraint for sustainable molluscan aquaculture. Development of strategies to enhance disease resistance during grow out would greatly reduce stock mortality and boost production yields. In this study, New Zealand black-footed abalone (Haliotis iris) were fed a commercial diet enhanced with multi-strain probiotics (Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc) for four months, then challenged with an injection of pathogenic Vibrio splendidus. Host immune responses in haemocytes were characterized using flow cytometry by measuring total haemocyte counts (THC) and viability, degree of apoptosis, and production of reactive oxygen species (ROS) 48 h post-challenge. Probiotic-fed abalone had significantly higher survival rates compared to control animals after the bacterial challenge. Infected probiotic-fed abalone also had significantly higher haemocyte viabilities, slightly lower proportions of haemocytes undergoing early apoptosis, and lower proportions of ROS-producing haemocytes compared to infected control-fed abalone. In addition, metabolite profiles of muscle tissues generated via gas chromatography-mass spectrometry (GC-MS) delivered complimentary evidence to support a perturbed ROS-regulatory system in infected abalone through changes in key metabolites associated with glutathione biosynthesis. The results of this study provide valuable information to assist in farm management practices, leading to enhance production and sustainability of the New Zealand abalone aquaculture industry.

Genetic features of Haliotis discus hannai by infection of vibrio and virus

BACKGROUND

Haliotis discus hannai more commonly referred to as the Pacific Abalone is of significant commercial and economical value in South Korea, with it being the second largest producer in the world. Despite this significance there is a lack of genetic studies with regards to the species. Most existing studies focused mainly on environmental factors.

OBJECTIVE

To provide a comprehensive review describing the genetic feature of Haliotis discus hannai by infection of vibrio and virus.

METHODS

This review summarized the immune response in the Haliotis spp. with regards to immunological genes such as Cathepsin B, C-type lectin and Toll-like receptors. Genetic studies with regards to transposable elements and miRNAs are few and far between. A study identified LTR retrotransposon Ty3/gypsy in the species. As to miRNA, a single study identified numerous miRNAs in the Haliotis discus hannai.

CONCLUSION

This paper sought to provide an overview of genetic perspective with regards to immune response genes, transposable elements and miRNAs.

Multi-strain probiotics enhance immune responsiveness and alters metabolic profiles in the New Zealand black-footed abalone (Haliotis iris)

We assessed whether dietary administration of a multi-strain probiotic (Exiguobacterium JHEb1, Vibrio JH1 and Enterococcus JHLDc) lead to enhanced immune responsiveness in juvenile New Zealand black-footed abalone (Haliotis iris). Two groups of abalone were fed (1% body weight per day) over a four-month period with different diets. The control diet consisted of a standard commercial pellet feed (AbMax 16), whereas the treatment diet was additionally enriched with the probiotic mix. At the end of the experiment, probiotic-fed animals showed improved growth compared with control-fed abalone in length (32.3% vs 22.3%), width (31.9% vs 20.7%) and wet weight (109.6% vs 72.8%), respectively. Haemolymph sampling was conducted at the beginning of the experiment and after 2 and 4 months. Haemolymph samples were analysed for total haemocyte count (THC) and viability, presence of apoptotic cells and production of Reactive Oxygen Species (ROS). Compared with control abalone, probiotic-fed abalone had significantly higher THC (1.9 × 10⁶ vs 5.6 × 10⁵ cells), higher viability (90.8% vs 75.6%), higher percentage of ROS-positive cells (19.4% vs 0.5%) and higher numbers of non-apoptotic cells (88.0% vs 78.0%), respectively. These results indicate that the probiotic-enriched diet enhanced the immunostimulatory mechanisms, with a simultaneous low-level up-regulation of ROS production as a priming mechanism of the antibacterial defence system. Metabolomics-based profiling of foot muscle tissue additionally revealed that probiotic-fed abalone differentially expressed 17 unique metabolites, including amino acids, fatty acids and TCA cycle related compounds. These data suggest that the probiotic-supplemented diet can also alter central carbon metabolic processes, which may improve the survival, as well as the growth of abalone.

Actibacter haliotis sp. nov., isolated from the gut of an abalone, Haliotis discus hannai, and emended description of the genus Actibacter

A novel strain, designated strain W113T, was isolated from the gut of an abalone, Haliotis discus hannai, which was collected from the northern coast of Jeju in Korea. The isolate was a Gram-staining-negative, facultatively anaerobic, non-motile, rod-shaped bacterium producing yellow-to-orange carotenoid-type pigments. 16S rRNA gene sequence analysis showed that the isolate belonged to the genus Actibacter in the family Flavobacteriaceae and it shared the highest sequence similarity with the type strain of Actibacter sediminis (98.8 % similarity). Optimal growth occurred at 25 °C, at pH 7 and with 2 % (w/v) NaCl. The major cellular fatty acids were iso-C15 : 0, anteiso-C15 : 0 and iso-C15 : 1 G. Menaquinone-6 was the main respiratory quinone. The polar lipids of the isolate were phosphatidylethanolamine, three unidentified amino lipids, and three unidentified lipids. The genomic DNA G+C content was 42.6 mol% and DNA–DNA hybridization values indicated that the strain shared <18 % genomic relatedness with the most closely related species. The results of the phylogenetic, phenotypic and genotypic analyses indicated that strain W113T represents a novel species in the genus Actibacter , for which the name Actibacter haliotis sp. nov. is proposed. The type strain is W113T ( = KACC 17209T = JCM 18868T).

Vibrio harveyi adheres to and penetrates tissues of the European abalone Haliotis tuberculata within the first hours of contact

Vibrio harveyi is a marine bacterial pathogen responsible for episodic epidemics generally associated with massive mortalities in many marine organisms, including the European abalone Haliotis tuberculata. The aim of this study was to identify the portal of entry and the dynamics of infection of V. harveyi in the European abalone. The results indicate that the duration of contact between V. harveyi and the European abalone influences the mortality rate and precocity. Immediately after contact, the epithelial and mucosal area situated between the gills and the hypobranchial gland was colonized by V. harveyi. Real-time PCR analyses and culture quantification of a green fluorescent protein-tagged strain of V. harveyi in abalone tissues revealed a high density of bacteria adhering to and then penetrating the whole gill-hypobranchial gland tissue after 1 h of contact. V. harveyi was also detected in the hemolymph of a significant number of European abalones after 3 h of contact. In conclusion, this article shows that a TaqMan real-time PCR assay is a powerful and useful technique for the detection of a marine pathogen such as V. harveyi in mollusk tissue and for the study of its infection dynamics. Thus, we have revealed that the adhesion and then the penetration of V. harveyi in European abalone organs begin in the first hours of contact. We also hypothesize that the portal of entry of V. harveyi in the European abalone is the area situated between the gills and the hypobranchial gland.

Actinomyces haliotis sp. nov., a bacterium isolated from the gut of an abalone, Haliotis discus hannai

A novel, Gram-staining-positive, facultatively anaerobic, non-motile and coccus-shaped bacterium, strain WL80T, was isolated from the gut of an abalone, Haliotis discus hannai, collected from the northern coast of Jeju in Korea. Optimal growth occurred at 30 °C, pH 7–8 and with 1 % (w/v) NaCl. Phylogenetic analyses based on the 16S rRNA gene sequence revealed that strain WL80T fell within the cluster of the genus Actinomyces , with highest sequence similarity to the type strains of Actinomyces radicidentis (98.8 % similarity) and Actinomyces urogenitalis (97.0 % similarity). The major cellular fatty acids were C18 : 1ω9c and C16 : 0. Menaquinone-10 (H4) was the major respiratory quinone. The genomic DNA G+C content of the isolate was 70.4 mol%. DNA–DNA hybridization values with closely related strains indicated less than 7.6 % genomic relatedness. The results of physiological, biochemical, chemotaxonomic and genotypic analyses indicated that strain WL80T represents a novel species of the genus Actinomyces , for which the name Actinomyces haliotis sp. nov. is proposed. The type strain is WL80T ( = KACC 17211T = JCM 18848T).

Shimia haliotis sp. nov., a bacterium isolated from the gut of an abalone, Haliotis discus hannai

A novel Gram-stain-negative, motile, rod-shaped bacterium, designated strain WM35T, was isolated from the intestinal tract of an abalone, Haliotis discus hannai, which was collected from the northern coast of Jeju in Korea. The cells of the isolate grew optimally at 30 °C, pH 7, and with 3 % (w/v) NaCl. Based on 16S rRNA gene sequence similarity comparisons, strain WM35T was grouped in the genus Shimia and was closely related to the type strains of Shimia isoporae (98.7 % similarity) and Shimia marina (97.8 % similarity). The major cellular fatty acids were summed feature 8 and C16 : 0 2-OH. Ubiquinone Q-10 was the predominant respiratory quinone. The polar lipids of strain WM35T comprised phosphatidylcholine, phosphatidylglycerol, diphosphatidylglycerol, an unidentified aminolipid and an unidentified lipid. The DNA G+C content of the isolate was 53.8 mol%. DNA–DNA hybridization values indicated <16 % genomic relatedness with members of the genus Shimia . The physiological, chemical and genotypic analyses indicated that strain WM35T represents a novel species of the genus Shimia , for which the name Shimia haliotis sp. nov. is proposed. The type strain is WM35T ( = KACC 17212T = JCM 18870T).

Cloacibacterium haliotis sp. nov., isolated from the gut of an abalone, Haliotis discus hannai

A novel Gram-stain-negative, aerobic, non-motile, yellow-pigmented and rod-shaped bacterium, designated strain WB5(T), was isolated from the intestinal tract of an abalone, Haliotis discus hannai, collected from the northern coast of Jeju in Korea. The isolate grew optimally at 30 °C, at pH 7 and in the presence of 0.5 % (w/v) NaCl. Phylogenetic analyses based on 16S rRNA gene sequences indicated that strain WB5(T) was clustered in the genus Cloacibacterium and shared the highest sequence similarity with C. normanense (98.2 % similarity). The predominant fatty acids were iso-C15 : 0 and iso-C17 : 0 3-OH. Menaquinone-6 was the major respiratory quinone. The genomic DNA G+C content was 29.6 mol%. The DNA-DNA hybridization values indicated <22 % genomic relatedness with other members of the genus Cloacibacterium. The results of physiological, biochemical, chemotaxonomic and genotypic analyses showed that strain WB5(T) represents a novel species of the genus Cloacibacterium, for which the name Cloacibacterium haliotis sp. nov. is proposed. The type strain is WB5(T) ( = KACC 17210(T) = JCM 18869(T)).

Pseudoruegeria haliotis sp. nov., isolated from the gut of the abalone Haliotis discus hannai

A novel Gram-negative, aerobic, non-motile and rod-shaped bacterium, designated strain WM67(T), was isolated from the gut of an abalone (Haliotis discus hannai) collected from the northern coast of Jeju Island in Korea. Phylogenetic analyses based on the 16S rRNA gene sequence indicated that strain WM67(T) clustered in the genus Pseudoruegeria, and the highest sequence similarity was shared with Pseudoruegeria lutimaris (98.0 % similarity to the type strain). Optimal growth of the isolate occurred at 30 °C, pH 7-8 and with 1 % (w/v) NaCl. The major cellular fatty acids were summed feature 8 (C18 : 1ω7c and/or C18 : 1ω6c) and C16 : 0. Ubiquinone Q-10 was the major respiratory quinone. The polar lipids of strain WM67(T) comprised phosphatidylserine, phosphatidylcholine, phosphatidylglycerol, phosphatidylethanolamine, an unidentified glycolipid and three unidentified lipids. The genomic DNA G+C content was 66.5 mol%. DNA-DNA hybridization indicated <17 % genomic relatedness to other members of the genus Pseudoruegeria. The physiological, biochemical, chemotaxonomic and genotypic analyses indicated that strain WM67(T) represents a novel species of Pseudoruegeria, for which the name Pseudoruegeria haliotis sp. nov. is proposed. The type strain is WM67(T) ( = KACC 17214(T) = JCM 18872(T)).

Effects of dietary supplementation of probiotic Shewanella colwelliana WA64, Shewanella olleyana WA65 on the innate immunity and disease resistance of abalone, Haliotis discus hannai Ino

The effects of dietary administration of two probiotics, Shewanella colwelliana WA64 and Shewanella olleyana WA65, on the innate immunity of abalone (Haliotis discus hannai Ino), and survival of juvenile abalone challenged with Vibrio harveyi have been studied. Two groups of abalone were fed with three different diets: one control, and two diets supplemented with 10(9) cell g(-1) of probiotic WA64 (WA64 diet) and WA65 (WA65 diet) for up to four weeks. Results showed that abalone fed diets containing S. colwelliana WA64 and S. olleyana WA65 had led to an enhanced cellular and humoral immune response, notably higher haemocytes, respiratory burst activity, serum lysozyme activity and total protein levels were recorded after one week of probiotic administration. On the other hand, mortality after the challenges with V. harveyi in the group fed with control diet ranged from 77 to 80%, while mortality rates observed in the groups fed with diets supplemented with WA64 and WA65 ranged from 27 to 50% and 30-43%, respectively. The results demonstrated potential for S. colwelliana WA64 and S. olleyana WA65 to improve innate immunity and disease resistance in H. discus hannai.

Identification and characterization of Vibrio harveyi associated with diseased abalone Haliotis diversicolor

Mass mortality of farmed small abalone Haliotis diversicolor occurred in Fujian, China, from 2009 to 2011. Among isolates obtained from moribund abalones, the dominant species AP37 exhibited the strongest virulence. After immersion challenge with 106 CFU ml-1 of AP37, abalone mortalities of 0, 53 and 67% were induced at water temperatures of 20°C, 24°C, and 28°C, respectively. Following intramuscular injection, AP37 showed a low LD50 (median lethal concentration) value of 2.9 × 102 CFU g-1 (colony forming units per gram abalone wet body weight). The LT50 (median lethal time) values were 5.2 h for 1 × 106 CFU abalone-1, 8.4 h for 1 × 105 CFU abalone-1, and 21.5 h for 1 × 104 CFU abalone-1. For further analysis of virulence, AP37 was screened for the production of extracellular factors. The results showed that various factors including presence of flagella and production of extracellular enzymes, such as lipase, phospholipase and haemolysin, could be responsible for pathogenesis. Based on its 16S rRNA gene sequence, strain AP37 showed >98.8% similarity to Vibrio harveyi, V. campbellii, V. parahaemolyticus, V. alginolyticus, V. natriegens and V. rotiferianus, so it could not be identified by this method. However, multi-locus sequence analysis (MLSA) of concatenated sequences, including the rpoD, rctB, gyrB, toxR and pyrH genes, identified strain AP37 as V. harveyi. Phenotypic characters of AP37 were identified by API 20E. In antibiotic susceptibility tests, strain AP37 exhibited susceptibility to 7 antibiotics and resistance to 13. This is the first report of a V. harveyi-related species being linked with the mass mortality of adult abalone H. diversicolor in southern China.

Characterization of interleukin-1 receptor-associated kinase 1 binding protein 1 gene in small abalone Haliotis diversicolor

Interleukin receptor-associated kinase (IRAK)-1 binding protein 1 (IRAK1BP1) is a critical factor in preventing dangerous overproduction of proinflammatory cytokines by the innate immune system and in influencing the specificity of TLR responses. In this study, a first molluscan IRAK1BP1 gene, saIRAK1BP1, was cloned from the small abalone (Haliotis diversicolor). Its full-length cDNA sequence is 1047bp, with a 747bp open reading frame encoding a protein of 249 aa. The molecular mass of the deduced protein is approximately 28.1kDa with an estimated pI of 8.87, and shows highest identity (52%) to acorn worm Saccoglossus kowalevskii. Amino acid sequence analysis revealed that saIRAK1BP1 shares a conserved SIMPL domain. Quantitative real-time PCR was employed to investigate the tissue distribution of saIRAK1BP1 mRNA, and its expression in abalone under bacteria challenge and larvae at different developmental stages. The saIRAK1BP1 mRNA could be detected in all examined tissues, with the highest expression level in hemocytes, and was up-regulated in gills, kidneys and hemocytes after bacteria injection. Additionally, saIRAK1BP1 was constitutively expressed at all examined developmental stages. These results indicate that saIRAK1BP1 play an important role in the adult abalone immune system and might be essential in embryo and larval development in abalone.

A great leap forward in microbial ecology

Ribosomal RNA (rRNA) sequence-based molecular techniques emerged in the late 1980s, which completely changed our general view of microbial life. Coincidentally, the Japanese Society of Microbial Ecology (JSME) was founded, and its official journal "Microbes and Environments (M&E)" was launched, in 1985. Thus, the past 25 years have been an exciting and fruitful period for M&E readers and microbiologists as demonstrated by the numerous excellent papers published in M&E. In this minireview, recent progress made in microbial ecology and related fields is summarized, with a special emphasis on 8 landmark areas; the cultivation of uncultured microbes, in situ methods for the assessment of microorganisms and their activities, biofilms, plant microbiology, chemolithotrophic bacteria in early volcanic environments, symbionts of animals and their ecology, wastewater treatment microbiology, and the biodegradation of hazardous organic compounds.

Environmental determinants correlated to Vibrio harveyi-mediated death of marine gastropods

Vibrio harveyi is an emerging pathogen that causes mass mortality in a wide variety of marine animal species; however, it is still unclear which environmental determinants correlate V. harveyi dynamics and the bacterium-mediated death of marine animal life. We conducted a correlation analysis over a 5-year period (2003-2007) analysing the following data: V. harveyi abundance, marine animal mortality and environmental variables (seawater temperature, salinity, pH, chlorophyll a, rainfall and total viable bacterial counts). The samples were collected from a coastal area in northern Japan, where deaths of a marine gastropod species (Haliotis discus hannai) have been reported. Our analysis revealed significant positive correlations between average seawater temperature and average V. harveyi abundance (R = 0.955; P < 0.05), and between average seawater temperature and V. harveyi-mediated abalone death (R = 0.931; P < 0.05). Based on the regression model, n degrees C rise in seawater temperature gave rise to a 21(n)-fold increase in the risk of mortality caused by V. harveyi infection. This is the first report providing evidence of the strong positive correlation between seawater temperature and V. harveyi-mediated death of marine species.

Pathogenic Vibrio harveyi, in contrast to non-pathogenic strains, intervenes with the p38 MAPK pathway to avoid an abalone haemocyte immune response

Vibrio harveyi is a marine bacterial pathogen responsible for episodic abalone epidemics associated with massive mortalities in France, Japan, and Australia. The aim of this study was the understanding of a possible role of the p38 MAPK in abalone haemocyte responses towards this bacterium. First, the pathogenicity of different V. harveyi strains was compared in both immersion and injection trials, and clear differences were detected. The three strains, ORM4, 04/092, and 05/053, all isolated from moribund abalone, induced up to 80% mortalities in immersion or injection challenges (LD(50) (ORM4) = 2.5 x 10(2) CFU animal(-1)). The two strains, LMG 4044T and LMG 7890 were non-pathogenic towards abalone in immersion trials, and needed very high numbers for killing by intramuscular injections (LD(50) = 8.9 x 10(4) and 1.6 x 10(5) CFU animal(-1), respectively). To start unraveling the mechanism explaining these differences, the p38-MAPK, a keyplayer in antimicrobial immune response, was studied. The non-pathogenic strain, LMG 7890 can be eliminated by abalone haemocytes and induces haemocyte phagocytosis and high ROS production. With different concentrations of a p38-specific inhibitor, SB203580, p38 implication was shown. This inhibitor reduced phagocytosis and ROS induction leading to LMG 7890 proliferation. In the case of the pathogenic ORM4 which can not be eliminated by abalone haemocytes, no phagocytosis and ROS production was induced, and a retarded p38 activation was observed. Taken together, our results suggest that p38 MAPK modulation may be one of the ways of virulent V. harveyi to attack its host and escape abalone immune response.