Youlu Su

Studies on the isolation of Photobacterium damselae subsp. piscicida from diseased golden pompano (Trachinotus ovatus Linnaeus) and antibacterial agents sensitivity

An epizootic occurred among cultured golden pompano (Trachinotus ovatus); it involved mass mortality on fish farms in Linshui in Hainan province, China, in 2008. Diseased fish exhibited no obvious clinical signs, but pathological studies showed that nodules were scattered over the spleen and kidney. To investigate the nature of the pathogen, we studied the surviving fish, and a Gram-negative bacterium (designated strain TOS1) was isolated from the spleens of golden pompano. Pathogenicity assays revealed that TOS1 was virulent for golden pompano when they were challenged by intraperitoneal injection, and the lethal dose (LD(50)) was 1.1 × 10(6)colony forming units (CFU)g(-1). 16S rDNA gene sequence of TOS1 demonstrated high similarity (99%) to that of Photobacterium damselae subsp. piscicida. Phylogenetic analysis also showed a clear association of strain TOS1 with P. damselae subsp. piscicida, and this agreed with the results of morphological, physiological and biochemical identification. The results also showed that TOS1 was sensitive to norfloxacin, gentamicin, sulfamethoxazole/trimethoprim, neomycin, streptomycin and tetracycline, and was very sensitive to Psidium guajava and Atractylodes lancea (minimum bactericidal concentration, MBC=10(-6)g/mL). This paper describes a systematic study of P. damselae subsp. piscicida isolated from diseased golden pompano in China, including its sensitivity to different antibiotics and Chinese herbal extracts, which will contribute to the diagnosis and prevention of the associated disease.

Identification of a cobia (Rachycentron canadum) CC chemokine gene and its involvement in the inflammatory response.

The chemokines regulate immune cell migration under inflammatory and physiological conditions. We investigated a CC chemokine gene (RcCC1) from cobia (Rachycentron canadum). The full-length RcCC1 cDNA is comprised 673 nucleotides and encodes a four-cysteine arrangement 99-amino-acid protein typical of known CC chemokines. The genomic DNA of RcCC1 consists of three exons and two introns. Phylogenetic analysis showed that RcCC1 was closest to the MIP group of CC chemokines. Quantitative real-time RT-PCR (qRT-PCR) analysis revealed RcCC1 was constitutively expressed in all tissues examined, with relative strong expression in gill, blood, kidney, spleen, and head kidney. The RcCC1 transcripts in the head kidney, spleen, and liver were quickly up-regulated after stimulation with formalin-inactivated Vibrio carchariae (bacterial vaccine) or polyriboinosinic polyribocytidylic acid (poly I:C). These results indicate RcCC1 not only plays a role in homeostasis, but also may be involved in inflammatory responses to bacterial and viral infection.

Susceptibility of farmed juvenile giant grouper Epinephelus lanceolatus to a newly isolated grouper iridovirus (genus Ranavirus).

A ranavirus was isolated from the diseased farmed groupers (Grouper iridovirus in genus Ranavirus, GIV-R), Epinephelus hybrids (blotchy rock cod, Epinephelus fuscoguttatus ♀×giant grouper, Epinephelus lanceolatus ♂), in Sanya, Hainan, in July 2013. In this study, susceptibility of farmed juvenile giant grouper E. lanceolatus to GIV-R was determined by intraperitoneally injection. The cumulative mortality reached to 81% at 5 day post infection. Histologically, severe degeneration with massive pycnotic nuclei in spleen and kidney tissues was observed, and some small-size inclusion body-bearing cells (IBCs) existed in spleen. Hemorrhage and infiltration of inflammatory cells were presented in gill, liver and heart along with tissue degeneration and necrosis of varying severity. The results of immunohistochemistry analysis showed that the strongest immunolabellings were obtained from the kidney and spleen tissues, while intermediate intensity signals were observed in the heart, stomach, gill and liver tissues, and the weakest signals were obtained from the intestine and brain, but no signal was obtained in eyes. Electron microscopy revealed that spleen of moribund fish contained many viral particles in cytoplasm. Interestingly, in surviving fish, abnormal hypertrophic cells were observed in both splenic corpuscle and renal corpuscle, while no hypertrophic cell was observed in the other parts of spleen and kidney tissues. Moreover, immunolabellings only stained the hypertrophic cells in splenic corpuscle and renal corpuscle. This indicated that splenic corpuscle and renal corpuscle play an important role in GIV-R infection and replication.

A new species of Glugea Thélohan, 1891 in the red sea bream Pagrus major (Temminck & Schlegel) (Teleostei: Sparidae) from China

A new microsporidian species is described from farmed red sea bream Pagrus major (Temminck & Schlegel) (Teleostei: Sparidae). Large numbers of spherical whitish xenomas were observed throughout the visceral organs of the host. Histological examination showed that the microsporidia caused several xenomas that were embedded in the intestinal muscularis externa or submucosa. Light and transmission electron microscopy examination of the spores also revealed morphological features typical of species of Glugea Thélohan, 1891. This microsporidian parasite has two different types of mature spores: microspores and macrospores. The spores are elongate-ovoid, with a large posterior vacuole. The polaroplast is bi-partite, with anterior and posterior parts comprising densely packed lamellae and loose membranes, respectively, and occupies approximately the anterior half of the spore. The polar filament is anisofilar, with 12–13 coils in a single layer almost touching the posterior spore wall. Comparison of the small subunit rDNA sequences revealed 92.7–98.1% identity with the sequences available from other Glugea spp. from piscine hosts. Phylogenetic analysis demonstrated that the microsporidian species studied clustered within the Glugea clade with strong support. Based on the differences in the morphological characteristics and molecular data, the microsporidian infecting P. major is considered to represent a species new to science, Glugea pagri n. sp.

Functional annotation of an expressed sequence tag library from Haliotis diversicolor and analysis of its plant-like sequences.

The small abalone, Haliotis diversicolor, is a widely distributed and cultured species in the subtropical coastal area of China. To identify and classify functional genes of this important species, a normalized expressed sequence tag (EST) library, including 7069 high quality ESTs from the total body of H. diversicolor, was analyzed. A total of 4781 unigenes were assembled and 2991 novel abalone genes were identified. The GC content, codon and amino acid usage of the transcriptome were analyzed. For the accurate annotation of the abalone library, different influencing factors were evaluated. The gene ontology (GO) database provided a higher annotation rate (69.6%), and sequences longer than 800bp were easily subjected to a BLAST search. The taxonomy of the BLAST results showed that lancelet and invertebrates are most closely related to abalone. Sixty-seven identified plant-like genes were further examined by reverse transcription-polymerase chain reaction (RT-PCR) and sequencing, only seven of these were real transcripts in abalone. Phylogenic trees were also constructed to illustrate the positions of two Cystatin sequences and one Calmodulin protein sequence identified in abalone. To perform functional classification, three different databases (GO, KEGG and COG) were used and 60 immune or disease-related unigenes were determined. This work has greatly enlarged the known gene pool of H. diversicolor and will have important implications for future molecular and genetic analyses in this organism.

Quantitative PCR detection for abalone shriveling syndrome-associated virus.

Haliotis diversicolor (small abalone) is an important seafood found along the southern coast of China. Since 1999, the yields of cultured abalone in China have been severely affected by an epidemic of continuous outbreaks of a fatal disease. A novel double-stranded DNA virus, abalone shriveling syndrome-associated virus (AbSV), was proven to be one of the main causative agent. Although the pathogenicity and genome of AbSV has been ascertained, the epidemiology of AbSV remains to be investigated. In this study, four pairs of AbSV-specific primers were designed on the basis of the AbSV genome, and were tested for their specificities and sensitivities in quantitative real-time PCRs (qPCRs) after optimization of the annealing temperature. The 3F3/3B3 primer pair was finally chosen with a good specificity and high efficiency of amplification, with a detection limit of about 10 copies of recombinant plasmid containing AbSV genes in a 20-μL reaction mixture. In the detection of AbSV in abalone samples along the southern coast of China, most of the diseased samples had more than 80 virus copies in 1ng host genome DNA. AbSV was also demonstrated in mature hybrid (LY) and juvenile (JH) abalones from assays of healthy animals collected in recent years.

Rapid detection of mud crab dicistrovirus-1 using loop-mediated isothermal amplification

Mud crab dicistrovirus-1 (MCDV-1) was isolated from the mud crab (Scylla paramamosain), resulting in mass mortality and widespread economic loss in China. In this study, a detection method for MCDV-1 using loop-mediated isothermal amplification was developed. Two pairs of primers targeting the VP2 gene were designed. These primers were the outer primers F3 and B3, and the inner primers FIP and BIP. Optimal amplification was carried out using 0.2 μmol/L F3/B3, 1.6 μmol/L FIP/BIP, 6 mmol/L Mg(2+), 0.8 mmol/L dNTPs, and 0.8 mol/L betaine, and completed in 1h at 62°C. The products demonstrated a ladder pattern on agarose gel electrophoresis and could also be detected visually according to turbidity, or by adding SYBR Green I and observing a color change from orange to green. The proposed method could specifically amplify MCDV-1 gene fragments. Sensitivity assay revealed that six copies of the viral genome could be detected by this method, which was 1000-fold more sensitive than that of conventional PCR using constructed plasmid as amplification template. At clinical sample level, sensitivity of LAMP was 100-fold higher than that of conventional PCR.

Characterization and transcriptional analysis of a new CC chemokine associated with innate immune response in cobia (Rachycentron canadum)

Chemokines are small, secreted cytokine peptides, known principally for their ability to induce migration and activation of leukocyte populations under both pathological and physiological conditions. On the basis of previously constructed express sequence tags (ESTs) of the head kidney and spleen cDNA library of the perciform marine fish Rachycentron canadum (common name cobia). We used bi-directional rapid amplification of cDNA ends (RACE) and obtained a full-length cDNA of a new CC chemokine gene (designated RcCC3). The RcCC3 putative peptide exhibits sequence similarity to the group of CCL19/21/25 CC chemokines. The reverse transcription quantitative polymerase chain reaction (RT-qPCR) was used in transcript expression studies of RcCC3. We examined the constitutive expression of the transcripts in 12 tissues of non-stressed cobia; RcCC3 transcripts were detected in all tissues examined, with the highest expression in gill and liver, following by head kidney, kidney, spleen, skin, intestine, muscle, stomach, heart, blood and brain. Transcript expression of RcCC3 was examined in immune-related organs, including head kidney, spleen and liver, following intraperitoneal injection of phosphate-buffered saline (control), polyriboinosinic polyribocytidylic acid (poly(I:C)) and formalin-killed Vibrio carchariae (bacterial vaccine). The transcripts in these tissues were quickly up-regulated by the injection of poly(I:C) and bacterial vaccine at early time points, although with different expression profiles. These results indicate RcCC3 represents an important component of innate immunity in cobia.

Nested PCR detection of abalone shriveling syndrome-associated virus in China.

Haliotis diversicolor (small abalone) is an economic seafood found off the Southern coast of China. Since 1999, the cultured abalone yields in China have been affected severely by continual outbreaks of a fatal epidemic disease caused by abalone shriveling syndrome associated virus (AbSV), a double-stranded DNA virus. Although the pathogenicity and genome of AbSV have been ascertained, the epidemiology of AbSV infection remains to be investigated. In the present study, four pairs of AbSV-specific primers were designed on the basis of open reading frame (ORF)24 and ORF25 sequences in the AbSV genome. Two nested PCR detection methods were established by optimization of the annealing temperatures of primers. The results showed that the specificity of primers for AbSV detection could not be interfered with by the host genome and other aquaculture species or viruses. The detection limits of the two methods were about 10 copies of recombinant plasmid containing AbSV genes in 20μL reaction mixture. The results of detection of the AbSV epidemic showed that AbSV was still present in juvenile abalones in some farms along the Southern coast of China (Fujian and Guangdong).

Mudworm Polydora lingshuiensis sp. n is a new species that inhabits both shell burrows and mudtubes.

A new polydorin species, Polydora lingshuiensis sp. n., which is found not only in burrows of pearl oyster shells (shell-boring type) but also in mudtubes on the surface of pearl oyster cages (tube-dwelling type), is described with the use of light microscopy, scanning electron microscopy, and molecular phylogeny. Morphological and molecular distinctions between P. lingshuiensis and other related species reveal that P. lingshuiensis is a valid new species. The reproduction characteristic that the eggs of P. lingshuiensis are gathered together in one hollow cylinder is another piece of evidence confirming that it is indeed a valid new species. Sequence comparisons based on nuclear 18S rDNA, 28S rDNA, and mitochondrial 16S rDNA show that strains of the shell-boring type possess as high as 99.9% to 100% sequence identity relative to those of the tube-dwelling type. This finding evidently indicates that these species types are conspecific. We also find that a comparison of mitochondrial 16S rDNA sequences can provide a higher resolution of polydorin species than those of the nuclear 18S rDNA because the former has a higher interspecific/intraspecific difference ratio. Phylogenetic analyses based on 18S rDNA sequences indicate that all P. lingshuiensis samples group together to forming a sister clade to Polydora uncinata and thus fall within Polydora aura/P. uncinata clade.