Analytical detection of parasite infection of Dinophysis norvegica using FISH probes

Abstract

Parasites of the genus Amoebophrya infect several free-living dinoflagellates, including harmful species. Whereas advanced infection can be easily detected, earlier stages of infection are more difficult to establish. rRNA-based fluorescent in situ hybridisation (FISH) probes specific to Amoebophrya sp. infecting Dinophysis norvegica in the Baltic Sea were combined with 4',6-diamidino-2-phenylindole (DAPI) staining to study this host-parasite system in a series of samples collected over a 24h period in August 1998. Small forms of Amoebophrya sp. (6–8μm) within D. norvegica, undetected by DAPI staining, were revealed by the FISH probe. As a result, the average infection estimated by FISH (7.8%) was 6.5 times higher than the estimate based on DAPI alone. Multiple infections were observed in 75% of the infected D. norvegica cells, indicating that this may be a common feature in this host-parasite system. FISH probes therefore provide a valuable tool to assess parasite infection of dinoflagellates in field samples.