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Epinecidin-1 is an antimicrobial peptide and plays a vital role in protecting fish against pathogenic infection. As a mimic of a grouper epinecidin-1 peptide, it has tertiary structures that closely resemble those of pleurocidin found in the winter flounder (Pleuronectes americanus). The tissue-specific, lipopolysaccharide (LPS)-stimulation-specific, and poly(I):poly(C)-stimulation-specific expressions of the grouper (Epinephelus coioides) epinecidin-1 antimicrobial peptide were determined using a comparative reverse-transcription polymerase chain reaction. Results of the tissue distribution analysis revealed high levels of epinecidin-1 messenger RNA (mRNA) in the head kidneys, intestines, and skin. Expression of epinecidin-1 mRNA was dose-dependently stimulated by both LPS and poly(I):poly(C). Immunohistochemical analysis with the polyclonal antiserum of a grouper epinecidin-1 peptide (rabbit polyclonal antibody) showed that the peptide was localized with the epinecidin-1 antibody in the gills and intestines. Two synthetic peptides of the grouper epinecidin-1 peptide (g-ple 22-51 and g-ple 22-42) and one winter flounder pleurocidin as a control exhibited high antimicrobial activities against gram-negative or gram-positive bacteria. In addition, peptide treatment was effective in promoting a significant increase in fish survival after the injection of Vibrio vulnificus in tilapia (Oreochromis mossambicus) and grouper. These results are relevant to the design of prophylactic and therapeutic strategies to counter bacterial infections, especially for preventing or ameliorating immune defects in fish during bacterial infections.

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The first isolation of Vibrio vulnificus in southern Taiwan from hybrid tilapia Oreochromis sp. raised in freshwater and brackish water environments is documented in this report. The infection was only found in fish in ponds where the salinity was less than 10 ppt. Tilapia raised in water of higher salinities in the same region were not affected. Grossly visible signs of infection included dark coloration, lethargy, and external hemorrhage and ulceration of the skin. The most prominent internal signs of infection included splenomegaly and severe hemorrhagic lesions in the liver. Septicemia was documented in moribund fish. All bacterial isolates from moribund fish were tested by polymerase chain reaction, using V. vulnificus hemolysin/cytolysin gene‐specific primers. Sequence data from the 16S ribosomal RNA gene suggest that these isolates were V. vulnificus. The isolates were indole and mannitol positive, characteristics shared by human clinical isolates and isolates from freshwater European eel, Anguilla anguilla. The isolates from tilapia were unique in that they were negative for ornithine decarboxylase and citrate.

Polybrominated diphenyl ethers (PBDEs) were applied as flame retardant additives in polymers for many plastic and electronic products. Due to their ubiquitous distribution in the environment, potential toxicity to human and tendency for bioaccumulation, PBDEs have raised public safety concern. In this study we examined the degradation of 4-monobrominated diphenyl ether (4-BDE) in aerobic sludge, as a model for PBDE biodegradation. Degradation of 4-BDE was observed in aerobic sludge. Co-metabolism with toluene or diphenyl ether facilitated 4-BDE biodegradation in terms of kinetics and efficiency. Diphenyl ether seems to perform slightly better as an auxiliary carbon source than toluene in facilitating 4-BDE degradation. During the experiment we identified diphenyl ether by gas chromatography/mass spectrometry(GC/MS), which indicates that an anaerobic debromination has occurred. Bacterial community composition was monitored with denaturing gradient gel electrophoresis. The fragments enriched in 4-BDE-degrading aerobic sludge samples belong to presumably a novel anaerobic Clostridiales species distantly related to all known debrominating microbes. This suggests that 4-BDE biodegradation can occur in anaerobic micro-niche in an apparently aerobic environment, by a previously unknown bacterial species. These findings can provide better understandings of biodegradation of brominated diphenyl ethers and can facilitate the prediction of the fate of PBDEs in the environment.

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