Hongzhan Liu

Identification of the pathogens associated with skin ulceration and peristome tumescence in cultured sea cucumbers Apostichopus japonicus (Selenka)

The aquaculture of sea cucumbers Apostichopus japonicus (Selenka) has developed rapidly in China in recent years, but is increasingly affected by diseases such as skin ulceration and peristome tumescence. Previous studies on the pathogens causing these diseases focused largely on bacterial causes. In December 2008, we isolated four dominant bacterial species from lesions present in A. japonicus with the aforementioned diseases, from a farm in Yangkou (Qingdao, China). With two of these bacterial species, experimental infection of healthy A. japonicus resulted in the same disease symptoms that occurred in naturally infected A. japonicus. These two species were identified as Pseudoalteromonas sp. and Pseudoalteromonas tetraodonis. The early symptoms of infection for these bacterial species were ulcer spots on the dorsal skin and abdominal parapodia, followed by an increase in the number of ulcer spots or their merging into larger spots. Additionally, we isolated a spherical virus 100-250nm in diameter and with a bilayer capsule, from A. japonicus with another disease from four different farms. By experimental infection with crude extracts of the virus, healthy laboratory-acclimatized A. japonicus developed the same symptoms as in natural infected cases. The early symptoms of viral infection comprised a decrease in tentacle activity, decay of dorsal papillate podia, peristome tumescence and abdominal ulceration. Our study demonstrates that the bacteria and virus were both responsible for skin ulceration and peristome tumescence in A. japonicus, but resulted in different early disease symptoms.

Immune Efficacy of a Genetically Engineered Vaccine against Lymphocystis Disease Virus: Analysis of Different Immunization Strategies.

Here, we report the construction of a vaccine against lymphocystis disease virus (LCDV) using nucleic acid vaccination technology. A fragment of the major capsid protein encoding gene from an LCDV isolated from China (LCDV-cn) was cloned into an eukaryotic expression vector pEGFP-N2, yielding a recombinant plasmid pEGFP-N2-LCDV-cn0.6 kb. This plasmid was immediately expressed after liposomal transfer into the Japanese flounder embryo cell line. The recombinant plasmid was inoculated into Japanese flounder via two routes (intramuscular injection and hypodermic injection) at three doses (0.1, 5, and 15 μg), and then T-lymphopoiesis in different tissues and antibodies raised against LCDV were evaluated. The results indicated that this recombinant plasmid induced unique humoral or cell-mediated immune responses depending on the inoculation route and conferred immune protection. Furthermore, the humoral immune responses and protective effects were significantly increased at higher vaccine doses via the two injection routes. Plasmid pEGFP-N2-LCDV0.6 kb is therefore a promising vaccine candidate against LCDV in Japanese flounder.

Effect of sodium selenite on some enzymes of coelomic fluid to the immune response of holothurian Apostichopus japonicus

The aquaculture of the sea cucumber Apostichopus japonicus(Echinodermata,Holothuroidea)has been growing rapidly over recent years in China in response to increasing consumer demand.Indeed,it has become an important sector of the marine industry in Northern China.However,with rapid growth and the use of non-standard practices and culture techniques,epidemic diseases of A.japonicus now pose increasing problems to the industry.Therefore,the healthy aquaculture of A.japonicus is important.For a reasonable evaluation of selenium effect on sea cucumber aquaculture,using laboratory tests to simulate the sodium selenite treatment and virus infection conditions,the detection and observation of the sea cucumber body cavity fluid immune enzyme changes,pathological changes and the relative rate of protection were made.The results showed that:the change of immune enzymes in coelomic fluid of sea cucumbers under simulated sodium selenite treatments and bacteria infected conditions was tested in order to reasonably evaluate the influence of selenium on aquaculture diseases.Results indicated that the activities of superoxide dismutase(SOD),glutathione peroxidase(GPx),lysozyme(LYZ),phenoloxidase(PO)and alkaline phosphatase(ALP)in coelomic fluid rose after sodium selenite treatments were enhanced.However,SOD,GPX and LYZ activities first ascended and then declined,and PO and ALP activities showed continued rise under additional pathogen injection into sea cucumbers,but the increasing extent of ALP activity was reduced along with increased sodium selenite concentration,and total diseased incidence rose and relative percent survival decreased under the severe sodium selenite treatment.This suggested that applying sodium selenite with moderate concentration could enhance immunity of sea cucumber to bacterial infection,but infecting also aggravated immune damage of sea cucumber by sodium selenite stress.Therefore,the diseases of cultured sea cucumber can be alleviated by optimized use of selenium.

Complete mitochondrial genome of the Pseudopleuronectes yokohamae (Pleuronectiforll: Pleuronectidae).

Abstract In this study, the complete mitochondrial genome of the Pseudopleuronectes yokohamae was sequenced. The mitochondrial genome is 17 383 bp in length, consisting of 13 protein-coding genes, 2 ribosomal RNA genes (rRNAs), 22 transfer RNA genes (tRNAs) and a control region (D-loop). The gene order and composition of P. yokohamae mitochondrial genome was similar to that of most other vertebrates. Two rRNA genes for 12S rRNA (949 bases) and 16S rRNA (1716 bases) are located between tRNA-Phe (GAA) and tRNA-Leu (TAA) and separated by the tRNA-Val. The control region of P. yokohamae, is located after tRNA-Pro and found to be 1679 bp. The overall nucleotides base composition of the heavy strand is A (27.55%), T (26.45%), G (28.75%), C (17.26%). With the exception of the NADH dehydrogenase subunit 6 (ND6) and eight tRNA genes, all other mitochondrial genes are encoded on the heavy strand. The 22 tRNA genes could be folded into a typical clover-leaf secondary structure. The phylogenetic trees consistently show that P. yokohama, Kareius bicoloratus and Platichthys stellatus from the same genus clustered into one branch. The complete mitogenome sequence information of P. yokohamae would provide useful data for further studies on population genetics and molecular systematics.