해양의 플랑크톤과 viral haemorrhagic septicemia virus와의 상호작용에 관한 연구

Abstract

Planktons and viruses are the important biotic components in the marine and freshwater ecosystems, but there are only a few studies reported on the effects of co-existence of them. Some studies have reported that plankton might serve as a transmission vector for viral diseases. Therefore, this study aimed to investigate the interaction between some types of plankton and viral haemorrhagic septicemia virus (VHSV). In this study, two types of phytoplankton including Skeletonema costatum and Chlorella sp, and one type of zooplankton, Rotifer (Branchionus plicatilis) commonly used for feed in the laval stage of farmed fish. The phytoplankton and zooplankton were cultivated in F/2 medium at 20 ℃ and sterilized seawater at 25 ℃, respectively. Each phytoplankton at two different concentrations (105, 106 cells mL-1) were co-cultured with VHSV (105, 106 copies mL-1) at 20 ℃ for up to 16 days. Rotifer (50 ind. mL-1) was fed with Chlorella sp. (3.1 × 107 cells mL-1) co-cultured with VHSV (106 copies mL-1) and co-cultured with VHSV (105 copies mL-1) without plankton harbored at 20 ℃ for 3 days. The mixture of each plankton and VHSV was separated into supernatant and pellet after centrifugation (4000xg 5min at 20 ℃). From each subsample set, VHSV was quantified by real-time PCR, and also viral activity was analyzed using TCID50 method. Approximately 6.2 × 103, 5.2 × 103 copies of VHSV were measured in the pellet containing phytoplankton up to 4 days and the virus was active as each phytoplankton pellet showed 3.5 × 103, 5.2 × 103 TCID50 pellet-1, respectively. In Chlorella sp. co-cultured with VHSV, VHSV concentration in the pellet was decreased from 105 to 104 pellet-1 for 16 days. The virus concentration in rotifer that has been fed with co-culture of VHSV plus Chlorella sp. for 3 days were 101 and 103 copies rotifer-1 on day 1 and day 3, respectively. VHSV concentration in rotifer that has been co-cultured with VHSV without plankton harbored 104 and 105 rotifer-1 at day 1 and 3, respectively. Based on the results of this study, it seems that VHSV could internalized into Chlorella sp. although it is unable to proliferate inside the plankton. This study shows that plankton can act as a transmission vector for VHS, and virus in the marine environment could be accumulated in the upper trophic level and may be involved in disease transmission.