ARS | Publication request: DEVELOPMENT OF THE INSECT PATHOGENIC ALGA HELICOSPORIDIUM

Submitted to: Journal of Eukaryotic Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 17, 2005
Publication Date: May 20, 2006
Citation: Blaeske-Lietze, V.U., Shapiro, A.M., Denton, J.S., Botts, M., Becnel, J.J., Boucias, D.G. 2006. Development of the insect pathogenic alga helicosporidium. Journal of Eukaryotic Microbiology.

Interpretive Summary: Naturally occurring protozoan parasites of insects are under study to evaluate and develop these disease causing organisms as biological control agents. A new species of Helicosporidia has been found in black flies in Florida. Helicosporida are known from a number of arthropods, but fundamental knowledge on their life cycles, modes of transmission and taxonomic placement are incomplete. In this investigation we have conducted basic biological studies of this Helicosporidium sp. to enhance evaluation as a biological control agent.

Technical Abstract: This study examined the morphogenesis and replication dynamics of the different life stages (cysts, filamentous cells, vegetative cells) of Helicosporidium sp., a non-photosynthetic, entomopathogenic alga. The isolate (SjHe) used originated from an infected black fly larva. Filamentous cell transformation into vegetative cells and autosporulation during vegetative cell replication were observed under controlled in vitro conditions. The transformation process was initiated by a partial swelling of the filamentous cell along with the reorganization of the nuclear material. Two subsequent nuclear and cell divisions resulted in the release of four rod-shaped daughter cells, which divided into oval to spherical vegetative cells. These underwent several cycles of autosporogenic cell division. Multiply passaged vegetative cell cultures formed nonmotile, adherent cell clusters (palmelloid colonies). Vegetative replication dynamics were also observed in two experimental noctuid hosts. The average density of helicosporidial cells produced per microliter hemolymph exceeded cell concentrations obtained in vitro 15- and 46-fold in Spodoptera exigua and Helicoverpa zea, respectively. Cyst morphogenesis was only observed in the hemolymph, whereas no cysts differentiated at various in vitro conditions.