In vitro culture and developmental cycle of the parasitic dinoflagellate Hematodinium sp. from the blue crab Callinectes sapidus

SUMMARYHematodinium is a genus of parasitic dinoflagellates whose species have caused significant mortalities in marine crustacean fisheries worldwide. A species of Hematodinium infects the blue crab, Callinectes sapidus on the eastern seaboard of the USA. The mode of transmission of the parasite in blue crabs is unknown. We established several continuous in vitro cultures of Hematodinium sp. isolated from the haemolymph of infected blue crabs. One isolate has been continuously maintained in our laboratory through serial subcultivation for over 12 months, and is capable of infecting new hosts when inoculated into healthy crabs. Cells of the parasite undergo characteristic developmental changes in vitro consistent with the identifiable stages of Hematodinium sp.: filamentous trophonts, amoeboid trophonts, arachnoid trophonts and sporonts, sporoblasts, prespores and dinospores (macrospores and microspores). Additionally, we describe an unusual shunt in the life cycle wherein presumptive schizonts derived from arachnoid sporonts developed into filamentous and arachnoid trophonts that can then initiate arachnoid sporonts in new cultures. This may explain the rapid proliferation of the parasite in blue crab hosts. We also found that temperature and light intensity affected the growth and development of the parasite in vitro.

PREVALENCE AND PHYLOGENY OF PARASITIC DINOFLAGELLATES (GENUS Blastodinium) INFECTING COPEPODS IN THE GULF OF CALIFORNIA

Plankton samples collected from Bahía de La Paz, Baja California Sur, Mexico in June 2008 revealed infection of copepods by Blastodinium spp. Of eight copepod genera encountered in the samples, only one (Paracalanus) was parasitized by Blastodinium. Infection prevalence was low, 0.6 % to 2.0 %, with all parasitized individuals being females tentatively identified as Paracalanus parvus. All but one infected host examined during the study was parasitized by Blastodinium crassum, the sole exception being a Paracalanus cf. parvus infected by Blastodinium contortum. A phylogeny constructed using a dataset of ~1.3 Kb sequences of the small subunit ribosomal DNA gene of B. contortum and B. crassum from Bahía de La Paz and 36 other dinoflagellate sequences available in GenBank, including all available for Blastodinium, placed Blastodinium as a monophyletic clade deep within the Dinokaryota. Sequence divergence among B. contortum ex Paracalanus cf. parvus from Bahía de La Paz, B. contortum ex P. parvus from the Mediterranean Sea, B. contortum ex Clausocalanus arcuicornis, B. crassum ex P. cf. parvus from Bahía de La Paz, and B. navicula ex Corycaeus giesbrechti supported separation of the three parasites as distinct species. Prevalecencia y filogenia de dinoflagelados parásitos (género Blastodinium) que infectan copépodos en el Golfo de California Muestras de plancton recolectadas en junio de 2008 en la Bahía de La Paz, México, revelaron la infección de copépodos por Blastodinium spp. De ocho géneros de copépodos encontrados, solo Paracalanus estuvo parasitado por Blastodinium. El porcentaje de prevalecencia de infección fue bajo, de 0.6 % a 2.0 %. Todos los ejemplares parasitados fueron hembras, identificadas tentativamente como Paracalanus parvus. Los hospederos analizados durante este estudio, a excepción de uno, estuvieron parasitados por Blastodinium crassum, siendo la única excepción Paracalanus cf. parvus, el cual fue infectado por Blastodinium contortum. Se construyó la filogenia usando la base de datos de secuencias ~1.3 Kb de pequeñas subunidades de DNA ribosomal de los genes de B. contortum y B. crassum de La Bahía de La Paz, además de otras 36 secuencias disponibles en GenBank, incluyendo todo lo disponible de Blastodinium y colocando a Blastodinium como un grupo dentro de los Dinokaryota. La divergencia de las secuencias entre B. contortum ex Paracalanus cf. parvus de Bahía de La Paz, B. contortum ex P. parvus del Mar Mediterráneo, B. contortum ex Clausocalanus arcuicornis, B. crassum ex P. cf. parvus de Bahía de La Paz, y B. navicula ex Corycaeus giesbrechti respalda la separación de los tres parásitos como especies diferentes.