LvPPAE2 induced by WSV056 confers host defense against WSSV in Litopenaeus vannamei.

Viral immediate early (IE) genes encode regulatory proteins that are critical for viral replication. WSV056 is an IE protein of white spot syndrome virus (WSSV), an important pathogen of farmed shrimp. It targets the host Rb protein(s) and, according to a previous study, may enhance the replication of the viral genome. However, the ectopic expression of WSV056 in transgenic Drosophila melanogaster exerted an inhibitory effect on the replication of Drosophila C virus (DCV). Transcriptome study using Affymetrix GeneChip suggested that the enrichment of serine proteases (SPs) likely accounts for DCV inhibition in WSV056-overexpressing Drosophila. Injection of recombinant WSV056 to the WSSV natural host Litopenaeus vannamei enhanced the expression of the SP family member prophenoloxidase-activating enzyme 2 (LvPPAE2) and conferred shrimp with more resistance to WSSV infection. LvPPAE2 knockdown contributed to decreased expression of antimicrobial peptides LvAlf1 and LvLyz1, reduced hemolymph phenoloxidase activity, and increased virus load, suggesting that LvPPAE2 is involved in the host defense against WSSV infection. Taken together, these results suggest that wsv056 plays a role in restricting viral replication by inducing the SP-mediated immune responses in the host.

Vibrio zhuhaiensis sp. nov., isolated from a Japanese prawn (Marsupenaeus japonicus).

A Gram-negative, oxidase-positive, facultatively anaerobic bacterium, designated strain E20121, was isolated from the digestive tract of a Japanese prawn (Marsupenaeus japonicus) collected from the coastal sea water area of Zhuhai, Guangdong province, China. The new isolate was determined to be closely related to Vibrio ponticus DSM 16217(T), having 97.6 % 16S rRNA gene sequence similarity. Phylogenetic analysis based on recA, pyrH and rpoA also showed low levels of sequence similarities (72.6-96.6 %) with all species of the genus Vibrio. A multigene phylogenetic tree using concatenated sequences of the four genes (16S rRNA, rpoA, recA and pyrH) clearly showed that the new isolate is different from the currently known Vibrio species. DNA-DNA hybridization experiments revealed similarity values below 70 % with the closest related species V. ponticus DSM 16217(T). Several phenotypic traits enabled the differentiation of strain E20121 from the closest phylogenetic neighbours. The DNA G+C content of strain E20121 was determined to be 47.6 mol % and the major fatty acid components identified were C16:1ω7c and/or C16:1ω6c (39.8 %), C18:1ω7c (13.6 %) and C16:0 (9.6 %). Based on genotypic, phenotypic, chemotaxonomic, phylogenetic and DNA-DNA hybridization analyses, strain E20121 is proposed to represent a novel species of the genus Vibrio for which the name Vibrio zhuhaiensis sp. nov. is proposed. The type strain is E20121(T)(=DSM 25602(T) = CCTCC AB 2011174(T)).

Vibrio zhanjiangensis sp. nov., isolated from sea water of shrimp farming pond.

A Gram-negative, facultatively anaerobic, motile by means of single polar flagellum, rod-shaped marine bacterium, designated strain E414, was isolated from sea water collected from a farming pond rearing marine shrimp Litopenaeus vannamei in Zhanjiang, Guangdong province, PRC. The strain was able to grow in the presence of 0.5-6% (w/v) NaCl (optimally in 3-6% (w/v) NaCl), between pH 6 and 9 (optimally at pH 7-8), between 15 and 37°C (optimally at 25-30°C). Phylogenetic analysis based on 16S rRNA gene sequences locate strain E414 in the vicinity of the coralliilyticus clade within the genus Vibrio. DNA-DNA relatedness data and multigene phylogenetic analysis based on the concatenated sequences of four genes (16S rRNA, rpoA, recA and pyrH) clearly differentiated strain E414 from its closest phylogenetic neighbours. Analysis of phenotypic features, including enzyme activities and utilization and fermentation of various carbon sources, further revealed discrimination between strain E414 and phylogenetically related Vibrio species. The major fatty acid components are C(16:1)ω6c and/or C(16:1)ω7c (27.4%), C(18:1)ω7c and/or C(18:1)ω6c (19.3%) and C(16:0) (18.2%). The DNA G+C content of strain E414 was 38.7 mol%. Based on phenotypic, chemotaxonomic, phylogenetic and DNA-DNA relatedness values, it can be concluded that E414 should be placed in the genus Vibrio as representing a novel species, for which the name Vibrio zhanjiangensis sp. nov. is proposed, with the type strain E414 (=CCTCC AB 2011110(T) = NBRC 108723(T) = DSM 24901).

Regulation of shrimp PjCaspase promoter activity by WSSV VP38 and VP41B.

Members of the Caspase family play essential roles in apoptosis. In kuruma shrimp Marsupenaeus japonicus the caspase gene (PjCaspase) was previously found dramatically up-regulated in viral-challenged and -resistant shrimp, suggesting that PjCaspase plays an important role in protecting host from viral infection. In order to further delineate the transcriptional regulation of PjCaspase in response to viral infection, the promoter activity was confirmed by fusing the 5'-flanking promoter region of the PjCaspase gene to the enhanced green fluorescence protein (EGFP) gene and transformed to Trichoplusia ni High Five™ cell line. With streptavidin-bead pulldown assay, two envelope proteins VP38 and VP41B of white spot syndrome virus (WSSV) were found to bind to PjCaspase promoter in vitro. Luciferase reporter assay by cotransfection of PjCaspace promoter with VP38 or VP41B revealed that the proteins act as repressor and activator of PjCaspase transcription respectively. Our study suggested a potential role for the two WSSV proteins on shrimp PjCaspase regulation in response to WSSV challenge. To our knowledge this is the first report on WSSV envelope proteins found to be involved in gene regulation. These results provide insights into the molecular regulation of PjCaspase gene expression, which will be helpful for shrimp viral disease control.