Spores of O. pajunii.[Image credit: Marcin K. Dziuba]

Host Daphnia dentifera infected with O. pajunii (on the right) and uninfected host (on the left). The infection is visible as white clusters of cells spanning across the green gut of Daphnia. [Image credit: Marcin K. Dziuba]

Ordospora pajunii is a microsporidium infecting planktonic cladocera of the genus Daphnia and Ceriodaphnia. The infectious spores are ingested with food and penetrate the cells of the host gut lining. Once inside the host cell, they proliferate, form clusters of cells and eventually induce host cell lysis at the end of the life cycle. The species O. pajunii was described from a rock pool in Finland (de Albuquerque et al. 2022). This strain was isolated from infected Daphnia dentifera collected from Walsh Lake (Washtenaw County, Michigan, USA).

The O. pajunii - D. dentifera interaction is a promising model for studying shifts along the mutualism – parasitism gradient (Rogalski et al. 2021), and for transgenerational virulence (McIntire et al. 2023). Studying the genome helps establish O. pajunii - D. dentifera as a model system, and allows addressing more in-depth questions regarding the molecular mechanisms regulating these phenomena.