FISH probes for the detection of the parasitic dinoflagellate Amoebophrya sp. infecting the dinoflagellate Akashiwo sanguinea in Chesapeake Bay.

A comparison of the small subunit rRNA sequences of a Chesapeake Bay strain of the dinoflagellate Akashiwo sanguinea and the dinoflagellate Amoebophrya sp. parasitizing it revealed several potential target sites that could be used to detect the parasite through in situ hybridization. The fluorescence of probed cells under various conditions of hybridization was measured by using a spot meter on a Nikon UFX-II camera attachment so that the effect of various hybridization parameters on probe binding could be determined. Probes directed against both the junction between helices 8 and 11 and helix 46 could detect the parasite, although the helix 8/11 probe produced a stronger signal under the conditions tested. The fluorescence of the probed cells increased with increasing hybridization time up to approximately twelve hours. The background fluorescence was lower at the wavelengths used to detect Texas Red than at those used to detect fluorescein, so probed cells were more distinct when Texas Red was used as the label. Cells stored in cold paraformaldehyde for a year still bound the probes. Young stages of the parasite could be seen more readily after in situ hybridization than after protargol impregnation.

Infection of Gymnodinium sanguineum by the dinoflagellate Amoebophrya sp.: effect of nutrient environment on parasite generation time, reproduction, and infectivity.

Preliminary attempts to culture Amoebophrya sp., a parasite of Gymnodinium sanguineum from Chesapeake Bay, indicated that success may be influenced by water quality. To explore that possibility, we determined development time, reproductive output, and infectivity of progeny (i.e. dinospores) for Amoebophyra sp. maintained on G. sanguineum grown in four different culture media. The duration of the parasite's intracellular growth phase showed no significant difference among treatments; however, the time required for completion of multiple parasite generations did, with elapsed time to the middle of the third generation being shorter in nutrient-replete media. Parasites of hosts grown in nutrient-replete medium also produced three to four times more dinospores than those infecting hosts under low-nutrient conditions, with mean values of 380 and 130 dinospores/host, respectively. Dinospore production relative to host biovolume also differed, with peak values of 7.4 per 1,000 microm3 host for nutrient-replete medium and 4.8 per 1,000 microm3 host for nutrient-limited medium. Furthermore, dinospores produced by "high-nutrient" parasites had a higher success rate than those formed by "low-nutrient" parasites. Results suggest that Amoebophrya sp. is well adapted to exploit G. sanguineum populations in nutrient-enriched environments.

The phylogenetic position of Amoebophrya sp. infecting Gymnodinium sanguineum.

The small-subunit rRNA sequence of a species of Amoebophrya infecting Gymnodinium sanguineum in Chesapeake Bay was obtained and compared to the small subunit rRNA sequences of other protists. Phylogenetic trees constructed with the new sequence place Amoebophrya between the remaining dinoflagellates and other protists.

Ciliated protozoa of two antarctic lakes: analysis by quantitative protargol staining and examination of artificial substrates.

Planktonic and artificial substrate-associated ciliates have been identified in two perennially ice-covered antarctic lakes of the McMurdo Dry Valleys. Abundances estimated by quantitative protargol staining ranged from < 5 to 31690 cells l-1, levels that are comparable to those previously obtained using other methods. Nineteen ciliate taxa were identified from these lakes, with the most frequently encountered genera being Plagiocampa, Askenasia, Monodinium, Sphaerophrya and Vorticella. The taxonomic findings compare favorably with those of previous investigators; however four previously unreported genera were observed in both Lakes Fryxell and Hoare. The variability in the depth distributions of ciliates in Lake Fryxell is explained in terms of lake physicochemical properties and ciliate prey distributions, while factors related to temporal succession in the Lake Hoare assemblage remain unexplained. Local marine or temperate zone freshwater habitats are a more likely source than the surrounding dry valleys soils for present ciliate colonists in these lakes. Although the taxonomic uncertainties require further examination, our results suggest that ciliate populations in these antarctic lakes undergo significant fluctuations and are more diverse than was previously recognized.

A disease of freshwater fishes caused by Tetrahymena corlissi Thompson, 1955, and a key for identification of holotrich ciliates of freshwater fishes.

Tetrahymena corlissi, a free-living protozoan, apparently caused the death of large number of guppies (Poecilia reticulatus) and occasionally other fishes, in aquaria and hatcheries at several locations. Apparently the disease occurs when the fish and protozoan populations are both at a high level of density. The signs include white spots and epidermal damage. Histologically, T. corlissi could be seen in skin, muscle, and viscera; in some there was marked inflammation, in others there was little tissue reaction. A key is presented for the identification of invasive fish ciliates: Chilodonella, Hemiophrys, Ichthyophthirius, Ophryoglena, and Tetrahymena.