Soon Jeong Lee

Effects of daylength, irradiance and settlement density on the growth and reproduction of Undaria pinnatifida gametophytes

The effects of daylength, irradiance and spore settlement density on the growth, maturation and sporophyte production of Undaria pinnatifida (Harvey) Suringar gametophytes were examined using a factorial experimental design in culture. The growth of Undaria gametophytes increased with increasing daylength (8, 12 and 16 h), but the maximum fertility occurred at a daylength of 12 h followed by 8 and 16 h. Gametophytes grew better at the 16 h daylength under the same mean daily irradiance (MDI) of 20 μmol photons m−2 s−1. However, the fertility was higher at the short daylength (8 h), indicating that the maturation of U. pinnatifida gametophytes is influenced by daylength rather than by the MDI. Vegetative growth and sporophyte production of gametophytes were better at 60 μmol photons m−2 s−1 than at 30 μmol photons m−2 s−1 under a 8:16 h LD (Light: Dark) cycle, and their growth and maturation were density-dependant in 16 and 12 h daylength, respectively. These results suggest that the U. pinnatifida gametophytes require a certain amount of light for the growth and reproduction, and intraspecific competition occurred under the optimal growth and maturation conditions. However, the sporophyte recruits per unit has been enhanced with increasing spore settlement density at 8 and 12 h daylengths indicating that high settlement density gives a benefit for maintaining population, even though the sporophyte production of each female plant is inhibited. In conclusion, the vegetative growth, reproduction and sporophyte production of U. pinnatifida gametophytes are retarded at a low irradiance above growth saturation and a high settlement density, and are determined by daylength.

Detection of Ostreid Herpesvirus 1 from adult Pacific Oysters Crassostrea gigas Cultured in Korea

The presence of ostreid herpesvirus 1 (OsHV-1) and the percentage of viral DNA detected in Pacific oyster Crassostrea gigas adults were investigated monthly between May and November 2012 at three locations along the southern coast of Korea. Among 210 oysters examined by polymerase chain reaction (PCR) analysis, OsHV-1 DNA was detected in only one oyster collected in August. The low detection rate of OsHV-1 DNA was consistent with the lack of reported OsHV-1-associated disease in C. gigas cultured in Korea. The sequence of the present PCR product amplified with the C2/C6 primer pair was identical to that of OsHV-1 μVar except for one nucleotide, and the sequence amplified with Del36-37F2/Del36-37R showed a 605-bp deletion as in OsHV-1 μVar. Although these sequence data are insufficient to determine genotype, the results suggest that the herpesvirus detected was similar to OsHV-1 μVar. This is the first report on the presence of OsHV-1 in adult Pacific oysters cultured in Korea.

Simultaneous and Systemic Knock-down of Big Defensin 1 and 2 gene Expression in the Pacific Oyster Crassostrea gigas using Long Double-stranded RNA-mediated RNA Interference

Abstract RNA interference (RNAi)-mediated transcriptional knock-down of Crassostrea gigas big defensin 1 and 2 genes ( Cg -BigDef1 and Cg -BigDef2) was investigated. The cDNA sequences of Cg -BigDef1 and Cg -BigDef2 were identical, excluding an additional fragment of 20 nucleotides in Cg -BigDef1; thus, a long double-stranded RNA (dsRNA) targeting the mRNA of Cg -BigDef2 ef-fectively downregulated both Cg -BigDef2 and Cg -BigDef1. In addition, long dsRNA targeting green fluorescent protein (GFP) did not affect transcription of the two big defensin genes. These results suggest that the transcriptional downregulation of Cg -BigDef1 and Cg -BigDef2 was mediated by sequence-specific RNA interference (RNAi). Despite injection of long dsRNA targeting Cg -BigDef2 into only the adductor muscle, knock-down of Cg -BigDef1 and Cg -BigDef2 was observed in the adductor muscle, hemo -cytes, mantle, and gills, suggestive of systemic spread of RNAi in C . gigas . Furthermore, the inhibitory effect of dsRNA persisted until 72 h post-injection, indicative of a long-lasting RNAi-mediated knock-down of target genes.

Phenology of host Chondrus ocellatus with filamentous green endophyte infection

Monthly variations in gametophyte and tetrasporophyte biomass of Chondrus ocellatus Holmes, a commercial carragenophyte alga, were examined at wave-exposed and sheltered shore stations of Jungdori, Wando, Korea from September, 2013 to August, 2014. The frequency of infection of the fronds with a green filamentous endophyte was investigated and the endophyte was identified using tufA analysis. Biomass of C. ocellatus was significantly greater at the exposed shore (331.84 g wet wt. m-2) than at the sheltered shore (181 g wet wt. m-2); the average biomass was 259 g wet wt. m-2. Gametophyte biomass of C. ocellatus accounted for 64.25% of the total biomass (259 g wet wt. m-2); tetrasporophyte biomass was 93.05 g wet wt. m-2 (35.93%). Biomass was minimal in winter and maximal in summer at both stations and similar patterns were found for gametophyte and tetrasporophyte biomass. Frond lengths and weights of C. ocellatus were slightly greater at the exposed shore than at the sheltered shore. Fronds of C. ocellatus were infected by a green endophytic species, which grew in between the cortical and medullar tissue and was identified as Ulvella ramosa by tufA analysis. We conclude that the optimal harvesting period of the C. ocellatus field population in terms of biomass might be autumn, after the rapid growth period. Additional in-depth research on the endophytes, such as infection mechanism and frequency, should be performed in order to maintain and manage the field populations of C. ocellatus.

Detection of Fish Pathogenic Viruses in Seawater Using Negatively Charged Membranes

After an outbreak of viral disease in an aquafarm, release of virus (es) from infected fish into environmental seawater has been suspected. In the present study, we utilized a negatively charged membrane (HA type) as an efficient method for concentration and detection of fish pathogenic viruses, specifically, megalocytivirus and viral hemorrhagic septicemia virus (VHSV) present in field-collected seawater samples or inoculated into seawater artificially. Positively charged viruses adsorbed onto the negatively charged membrane and were eluted with 1 mM NaOH (pH 10.5) following rinsing with 0.5 mM (pH 3.0). Megalocytivirus and VHSV particles isolated using anegatively charged HA membrane from seawater inoculated with each virus at a concentration of 10 viral particles/mL were of sufficient quantity to show positive results in atwo-step PCR (or RT two-step PCR); however, despite it being negatively charged, a cellulose acetate (CA) membraneshowed negative results. In quantitative PCR, the detection limits of the HA membrane for megalocytivirus and VHSV in seawater were 1.20E+00 viral particles/mL and 1.22E+01 viralparticles/mL, respectively. The calculated mean recovery yields from 1 L seawater spiked with known concentrations of megalocytivirus and VHSV particles were 28.11% and 23.00%, respectively. The concentrate of a 1-L sample of culturing seawater from the aquatank of flounder suffering from VHSV showed clear positive results in PCR when isolated with an HA, but not a CA, membrane. Thus, viral isolation using an HA membrane is a practical and reliable method for detection of fish pathogenic viruses in seawater.