With the help of Next-Generation Sequencing (NGS) technology, comprehensive genomic and transcriptomic studies have been conducted by researchers working on mollusks around the world. Base on March 2020 data at the GOLD database, 237,877 genetic projects have been registered. It shows that these results are about 4 times higher than the data reported in 2015, meaning that the genetic projects have been steadily conducted with various species. Among them, a total of 71 cases were registered for mollusks (37 cases of bivalves, 28 cases of gastropoda, and 6 cases of cephalopoda). The genome project for mollusks has increased by about 30 cases compared to 2015, mainly in the United States and China. Besides, analysis of the genetic resources registered in the NCBI for ten years indicated that the genome projects have quadrupled depending on the type of database. In case of sequence read archive (SRA) database, 18,476 mollusks-related genomic studies (about 34.7 TB) have been registered. About 66 GB of data was registered by 2010, and also about 32,532 GB was registered from 2011 to 2019, meaning that there is a 500-fold increase over the decade. Taken together, it is expected that genomic research on mollusks will have many advantages such as the preemption of genetic resources.
Shellfish production on the west coast Korea has been declined for the past two decades, and the parasite infection is considered to be one of the causes responsible for the decline of Manila clam Ruditapes philippinarum. In this study, we first investigated the pathologic condition of Manila clams and the Pacific oysters Crassostrea gigas in Garorim Bay on the west coast, where Manila clams and the Pacific oysters are co-cultured. Histology and Ray’s fluid thioglycollate medium assay (RFTM) revealed that most of Manila clams are infected by protozoan parasite Perkinsus olseni (98.0-100.0% prevalence). In contrast, none of the Pacific oysters diagnosed by the histology showed P. olseni in their tissue. The mean infection intensity of P. olseni in Manila clams was high, ranging from 0.796 (Ohiji-ri) to 2.058 (Dangsan-ri) × 106 cells/g wet tissue weight. In histology, metacercaria of Parvatrema duboisi was identified from the mantle tissue of Manila clam. Ancistrocoma-like ciliates (ALCs) were found from the digestive tubules of the oysters, with the prevalence ranging from 10.0 to 13.0 %. Rickettsia-like organisms (RLOs) were commonly identified from the epithelial cells of the digestive tubule of the Pacific oysters and Manila clams, with a prevalence ranging from 0.0 to 10.0% in Manila clams and 6.7 to 10.0% in the oysters. The mean condition index (CI) of Manila clams from Ohji-ri was significantly lower than CI of clams at Dangsan-ri tidal flat (ANOVA, P < 0.05). The mean digestive gland atrophy (DGA) of clams at Ohji-ri was significantly higher than the DGA of clams at Dangsan-ri (ANOVA, P < 0.05). The mean infection intensity of P. olseni in the host clams from Dangsan-ri was significantly higher than the clams in Ohji-ri (ANOVA, P < 0.05). The observed spatial variation in the CI and DGA was believed to be linked to a spatial change in the available food in the environment, although more investigations must be carried out to validate this hypothesis.
In the present study, we developed the upwelling system for the culturing of cultchless juvenile oyster and evaluated its effect in indoor and outdoor sites. Indoor upwelling system was made by using 1 L transparent plastic imhoff cone to move seawater from bottom to top. Outdoor upwelling system was designed to continuously upward water flow into inside the tank by discharging the seawater from the upper part of the tank to the central drainage pipe. Indoor culture periods were 2 weeks, and outdoor culture periods were 35 days. During the experiments, water temperature, salinity, dissolved oxygen and pH were suitable for oyster culture. We cultured 1-8 mm cultchless juvenile oysters in the upwelling and downwelling system for 2 weeks in indoor. As a result, smaller oysters showed higher specific growth rate, and the weight increase was faster in the upwelling system. Subsequently, 9-32 mm juvenile oysters were cultured outdoors in upwelling system and off-bottom net cage facility for 35 days. As a result, it was found that there was a significantly higher in the total weight increase in the upwelling system. These indicate that the upwelling system is effective for cultchless juvenile oysters because it expands the use of seawater layers to increase food intake opportunities.
Antimicrobial peptides (AMPs) constitute important components of the innate immunity, protecting the host against infections. A synthetic antimicrobial peptide was identified as a possible candidate for the development of a new antibacterial drug. We previously developed novel AMPs derived from a lipopolysaccharide- and ß-1, 3-glucan-binding protein (LGBP) of the pacific abalone Haliotis discus hannai (HDH) particularly showing antimicrobial against bacteria and fungi and antitumor activities against several cancer cells.To evaluate in-vivo toxicity of AMPs is an essential step to ensure it safe use in drugs and foods. In the present study, we have investigated to evaluate in-vivo toxicity of HDH-LGBP in mouse when orally administered to both sexes of ICR mice (10 males and 10 females in each group) at dose of 50, 100 and 200 mg/kg/day for 14 days. Individual food/ water consumption and body weight changes were measured daily. The group treated with HDH-LGBP didn’t show any histological change in the kidney and liver. Statistically significant decreases of food consumption, serum creatinine and platelet were found in 200 mg HDH-LGBP-treated groups when compared to their respective controls. It was considered to be caused by stress and peptide gelation. Male and female mice did not show effects body weight, food consumption, organ weights, hematology, serum chemistry, urinalysis or microscopic pathology. Therefore, the no-observed-adverse-effect level (NOAEL) for HDH-LGBP was concluded to be a 200 mg/kg/day. These results corroborate the potential of this novel AMP (HDH-LGBP) as an alternative food preservative or multifunctional drug.
Charonia sauliae, the largest sea snail is designated as the class I endangered species of red list data in Korea, because of habitat destruction and environmental pollution. For the conservation and restoration of this species, identification of genetic resources through transcriptomic and genomic studies, and investigation of ecological information are needed. In this study, we identified aquaporin (AQP) which plays an essential role in the water channel, by local-blast analysis with the nucleotide database of C. sauliae generated by Illumina Hi-Seq 2000 next-generation sequencing platform. AQP of C. sauliae contained 897 bp of nucleotides encoding 299 amino acid residues. The domain analysis of AQP showed one aquaporin-like domain including six transmembrane domains, eight amino acid residues which are related to the amphipathic channel, and two Asn-Pro-Ala signature motifs (NPA boxes). 3-Dimensional analysis indicated that it included six alpha-helix structures, which formed the transmembrane channel. To understand the evolutionary-relationship of AQP, conducted the multiple alignments and phylogenetic analysis, resulting in that AQP contained highly conserved NPA boxes and transmembrane domain. AQP of C. sauliae was localized in the same branch with Pomacea canaliculata (Ampullariidae). In the future, our results provide valuable information for the functional characterization of marine invertebrate aquaporin.
The rate of marine pathogen spread is increasing because of the increase in ocean temperatures, transportation, ocean currents, and marine product trade worldwide. In Korean waters, several species of single-celled or metazoan pathogenic organisms have been identified that may hamper aquaculture or international trade of the Manila clam Ruditapes philippinarum. In this study, we reviewed the different types of pathogenic organisms isolated and reported from Manila clams worldwide. Among these pathogens, the diseases caused by two protozoan parasites, Perkinsus olseni and Marteilia refringens, are listed as OIE notifiable. P. olseni infection in Manila clam causes retarded growth and reproduction and mass mortality of the clam and has been reported in Korea, China, and Japan. M. refringens infection in Manila clams has been reported only once in China, although further information is unavailable. Trematode infections in the Manila clam often result in slow gonad maturation or gonad castration and may result in a decline in recruitment. The introduction of various invasive pathogens via the import of host organisms or discharge of ballast water of commercial shipping vessels may cause various ecological and evolutionary issues in the native ecosystem. Therefore, it is recommended to improve the quarantine methods of imported shellfishes and monitor the commercially important shellfish species in Korean waters to prevent the spread of exotic pathogenic organisms.