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In July 2010, heavy mortalities were seen in cultured swimming crabs, Portunus trituberculatus, from Jiangsu Province in China. Two isolates, XA1 and XA2, were isolated from cardiac muscle and somatic muscle of the moribund crabs on ZoBell's marine 2216E agar and were confirmed as the causative agent for the mass mortalities seen on that farm. The morphological and physiological characteristics as well as the biochemical tests of the two isolates were identical and were similar to Vibrio natriegens. Both were gram-negative, oxidase positive, produced acid when fermenting glucose, and failed to grow in the media containing 1% NaCl. Furthermore, the sequencing of the 16S rRNA, gapA, ftsZ, mreB, and topA genes revealed that the two isolates were identical and had a 0.99 homology coefficient with V. natriegens. The Neighbor-Joining tree based on the concatenated sequences of four housekeeping genes (gapA, ftsZ, mreB, and topA) strongly supported that XA1 was most closely related to V. natriegens within the Vibrio harveyi–related clade. In addition, pathogenicity testing using immersion challenge confirmed that strain XA1 was virulent to juvenile crabs, and the LD50 value was 1.09 × 106. This is the first report on V. natriegens as a virulent pathogen for Portunus trituberculatus.

2'-5'-Oligoadenylate synthetase-like protein (OASL) is an interferon-inducible antiviral protein that exerts antiviral effects through the RNase L- or retinoic acid-inducible gene I (RIG-I)-dependent signalling pathway. In this study, we identified and cloned the OASL gene (named duOASL) from healthy adult Cherry Valley ducks. Full-length duOASL cDNA (1630bp) encoded a 504-amino acid polypeptide containing three conserved domains, namely, nucleotidyltransferase domain, 2'-5'-oligoadenylate synthetase domain, and two ubiquitin-like repeats. DuOASL mRNA expression was quantified by performing quantitative reverse transcription-PCR (qRT-PCR). Results of qRT-PCR showed that duOASL was broadly expressed in all examined tissues, with the highest mRNA expression in the large intestine. Antiviral activity of duOASL was measured by determining its effect on Duck Tembusu virus (DTMUV) replication in vitro. We found that duOASL overexpression slightly inhibited DTMUV replication, whereas duOASL knockdown by using a specific small interfering RNA increased DTMUV replication in DF-1 cells. Thus, we successfully cloned and characterized the antiviral protein duOASL from Cherry Valley ducks and found that it exerted antiviral effects against DTMUV. These results provide a solid foundation for performing further studies to determine the mechanism underlying the antiviral effect of duOASL at the cellular level.

This study aimed to evaluate the survival and gene expression of Vibrio harveyi under starvation conditions. The microcosms V. harveyi were incubated in sterilized seawater for four weeks at room temperature. Overall, the cell numeration declined rapidly about 103 CFU/ ml during starvation, with a tiny rebound at day twenty-one. Scanning electron microscopy revealed rod-shaped cells became sphere with a rippled cell surface. By polymerase chain reaction (PCR) assay, nine genes, named lux R, tox R, vhh B, fla A, top A, fur , rpo S, mre B, fts Z were detected in the non-starvedi cells. In the starved, the expression levels of the detected genes declined substantially ranging from 0.005-fold to 0.028-fold compared to the non-starved performed by reverse transcription quantitative real-time polymerase chain reaction (RT-qPCR) with 16s rRNA as the internal control. In the recovering cells, the expression levels of the detected genes, except lux R and mre B, were upregulated dramatically compared to the wild, especially top A (23.720-fold), fur (39.400-fold) and tox R (9.837-fold), validating that the expressions of both the metabolism and virulence genes were important for growth and survival of V. harveyi. The results may shed a new light on understanding of stress adaptation in bacteria.