Parasites of QX-resistant and wild-type Sydney rock oysters (Saccostrea glomerata) in Moreton Bay, SE Queensland, Australia: diversity and host response.

Wild caught (WC) and QX resistant (QXR) Sydney rock oysters were introduced at North Stradbroke Island and Pimpama River, SE Queensland, Australia, and sampled monthly during 1 year. Three groups of parasites/diseases were identified by observation of histological sections: (1) Marteilia sydneyi (Queensland unknown (QX) disease) and Steinhausia sp. (Microsporidia) characterized by a high prevalence and deleterious impact on the host; (2) disseminated neoplasia and the trematode Proctoeces sp. characterized by low prevalence but deleterious effects on the host; (3) parasites or symbionts with no detectable effect on the host: trematodes, ciliates, turbellarians and metacestodes. Mortality rates were similar between both oyster lines but higher at Pimpama River (reaching around 90%) than Stradbroke Island, mostly because of QX disease and, to a lesser extent, to the unfavourable environmental conditions of the summer 2010-2011. Lower prevalences of QX disease at Stradbroke Island probably related to the relative lack of intermediate hosts of the parasite and to lower freshwater input. Surprisingly, no difference in prevalence of QX disease was observed between the two oyster lines.

Two hepcidin-like antimicrobial peptides in Barramundi Lates calcarifer exhibit differing tissue tropism and are induced in response to lipopolysaccharide.

Genes encoding two hepcidin-like antimicrobial peptides were discovered in Barramundi, Lates calcarifer (barramundi, Giant sea perch). Analysis of the coding regions indicated that genes for each hepcidin comprised 3 exons and 2 introns. The deduced amino acid sequences for each molecule resulted in a protein comprising a signal sequence of 24 aa in each case, coupled to a prepropeptide of 75 aa for hepcidin 1 and 78 aa for hepcidin 2. A cleavage site was identified in each prepropetide at amino acid 64 with the cleavage motif--QKR/QS--resulting in mature peptides of 25 and 28 amino acids respectively. Each mature peptide contained 8 conserved cysteine residues and 3 dimensional modeling predicted a ß-hairpin and ß-sheet structure characteristic of human Liver Expressed Antimicrobial Peptide (LEAP). Analysis of the deduced amino acid sequences by BLAST with phylogenetic supported indicated that hepcidin 1 was a HAMP1-type peptide closely related to hepcidins identified in other Perciformes (Micropterus and Pseudosciaena), whilst hepcidin 2 was a HAMP2-type peptide most similar to a hepcidin previously identified in black rock fish (Sebastes schlegeli). Both hepcidin genes were inducible in barramundi following intraperitoneal injection with lipopolysaccharide, with elevated expression detected in liver and head kidney 3 h post IP injection for hepcidin 1 and in liver only for hepcidin 2. The elevated expression was transient with return to normal levels within 24-48 h. No significant expression of either peptide was detected in spleen, skin or gill following IP injection with LPS.

Linear and branched beta(1-3) D-glucans activate but do not prime teleost macrophages in vitro and are inactivated by dilute acid: implications for dietary immunostimulation.

Beta(1-3) glucans are a diverse range of carbohydrate polymers of differing lengths and structures that make up the cell walls of yeast, fungi, algae and some plants and activate innate immune responses in plants, invertebrates and higher animals. Consequently glucans are often used as dietary immunostimulants in commercial feeds for aquacultured fish species. The present study investigates the capability of purified glucans of differing structures and configurations, including curdlan, paramylon, laminarin and purified yeast beta glucan to activate innate immunity in vitro using barramundi pronephros macrophages as a model, and compares them to Zymosan, a complex mixture derived from yeast cell walls, and lipopolysaccharide from Gram negative bacteria. All of the glucans were able to stimulate respiratory burst in barramundi macrophages at concentrations of 100 microg/mL and 1000 microg/mL, with curdlan eliciting the highest respiratory burst response at 1000 microg/mL. LPS and Zymosan were the only immunostimulants tested that could prime barramundi macrophages by incubating with low concentrations (0.1 and 1 microg/mL) for 24 h before triggering respiratory burst with PMA, suggesting teleost macrophages may not prime through the glucan receptor. As glucans are used as dietary immunostimulants, the pH of the barramundi stomach was assayed for 6 h following feeding and indicated that pH was as low as 2 for up to 6 h. Treating the glucans with dilute HCl at pH 2 completely neutralised their macrophage-activating capability. These results are important as they indicate that glucans do not prime barramundi macrophages but will activate them at high concentrations. However, it is debatable whether glucans will have any effect on macrophages if administered in the diet due to the combination of high concentration required and probable hydrolysis of the polymer structures as they pass through the acid environment of the stomach.

Differential expression of genes encoding anti-oxidant enzymes in Sydney rock oysters, Saccostrea glomerata (Gould) selected for disease resistance.

Sydney rock oysters (Saccostrea glomerata) selectively bred for disease resistance (R) and wild-caught control oysters (W) were exposed to a field infection of disseminating neoplasia. Cumulative mortality of W oysters (31.7%) was significantly greater than R oysters (0.0%) over the 118 days of the experiment. In an attempt to understand the biochemical and molecular pathways involved in disease resistance, differentially expressed sequence tags (ESTs) between R and W S. glomerata hemocytes were identified using the PCR technique, suppression subtractive hybridisation (SSH). Sequencing of 300 clones from two SSH libraries revealed 183 distinct sequences of which 113 shared high similarity to sequences in the public databases. Putative function could be assigned to 64 of the sequences. Expression of nine ESTs homologous to genes previously shown to be involved in bivalve immunity was further studied using quantitative reverse-transcriptase PCR (qRT-PCR). The base-line expression of an extracellular superoxide dismutase (ecSOD) and a small heat shock protein (sHsP) were significantly increased, whilst peroxiredoxin 6 (Prx6) and interferon inhibiting cytokine factor (IK) were significantly decreased in R oysters. From these results it was hypothesised that R oysters would be able to generate the anti-parasitic compound, hydrogen peroxide (H(2)O(2)) faster and to higher concentrations during respiratory burst due to the differential expression of genes for the two anti-oxidant enzymes of ecSOD and Prx6. To investigate this hypothesis, protein extracts from hemolymph were analysed for oxidative burst enzyme activity. Analysis of the cell free hemolymph proteins separated by native-polyacrylamide gel electrophoresis (PAGE) failed to detect true superoxide dismutase (SOD) activity by assaying dismutation of superoxide anion in zymograms. However, the ecSOD enzyme appears to generate hydrogen peroxide, presumably via another process, which is yet to be elucidated. This corroborates our hypothesis, whilst phylogenetic analysis of the complete coding sequence (CDS) of the S. glomerata ecSOD gene is supportive of the atypical nature of the ecSOD enzyme. Results obtained from this work further the current understanding of the molecular mechanisms involved in resistance to disease in this economically important bivalve, and shed further light on the anomalous oxidative processes involved.

Antibody increases phagocytosis and killing of Lactococcus garvieae by rainbow trout (Oncorhynchus mykiss, L.) macrophages.

The present study reports that specific antibody increased the bactericidal activity of rainbow trout head-kidney macrophages against virulent capsulated Lactococcus garvieae in the absence of complement. The observed increased bactericidal activity appeared to result from increased phagocytosis of capsulated L. garvieae in the presence of specific antibody and may in part explain the protective effect of antibody previously reported against this disease.

Invasion of fish epithelial cells by Photobacterium damselae subsp. piscicida: evidence for receptor specificity, and effect of capsule and serum.

Photobacterium damselae subsp. piscicida is a fish pathogen which causes serious disease in commercial warmwater fish species. Because information on the initial stages of the infection is scarce, an investigation of the invasion ability of this pathogen was undertaken utilizing a fish epithelial cell line (epithelioma papillosum carpio, EPC), a virulent capsulated strain of P. damselae (MT1415), an avirulent non-capsulated strain of P. damselae (EPOY-8803-ii) and Escherichia coli HB101 as a non-invasive control. P. damselae was found to be able to adhere to and invade fish epithelial cells and remain inside them for 6-9 h. There were no significant differences in invasiveness between the capsulated and non-capsulated strains. A kinetics study demonstrated that P. damselae invasiveness was more efficient at low m.o.i., reaching saturation at higher m.o.i., suggesting internalization may be receptor-mediated. Invasion efficiency (IE) was significantly higher than in the control E. coli HB101. Engulfment of bacteria was possibly by an endocytic process and was unaffected by killing the bacteria with UV light. However, heat-killed bacteria had significantly reduced invasion capability. Ultrastructural studies showed that inside the epithelial cells, the bacteria remained within large vacuoles for a few hours and no evidence of intracellular replication was found, by either fluorescence or electron microscopic studies. Normal sea bass serum slightly reduced the invasion capability of the MT1415 strain, but heat-inactivated normal serum had no effect. On the other hand, heat-inactivated fish antiserum raised against the same strain reduced the percentage of invaded epithelial cells by 50%. As for other pathogens, an intracellular phase of P. damselae may be a mechanism to delay or avoid phagocytosis and host immune responses, favouring the spread of infection.