Helicosporidium

Definition

A genus of colorless, achlorophyllous parasitic green algae in the class Trebouxiophyceae that infects the gut and other tissues of insects and other arthropods. Unlike its photosynthetic relatives in Chlorellaceae, Helicosporidium has lost chloroplasts and lives as an obligate intracellular parasite, producing distinctive helically coiled spores. It represents a rare evolutionary transition from autotrophy to heterotrophy within the green algae, paralleling the better-known genus Prototheca.

Etymology

From Greek helix (helix, spiral) + sporidium (small spore), referring to the helically coiled morphology of its dispersal spores.

Example

Helicosporidium parasiticum infects the midgut epithelium of mosquito larvae, causing cellular hypertrophy and mortality; the parasite's helical spores are diagnostic in wet-mount preparations of infected tissue.

Related Terms

• Prototheca
• Trebouxiophyceae
• Chlorellaceae
• achlorophyllous
• entomopathogen
• Microsporidia
• obligate parasite

Usage Notes

Distinguished from Microsporidia (fungal parasites) and Gregarinea (apicomplexan parasites) by its algal cell-wall composition and green-algal phylogenetic affinities. The helical spore morphology is distinctive but requires molecular confirmation for identification. Some species formerly classified here have been reassigned based on phylogenetic studies.