Summary auto-generated
Helicosporidium species are invertebrate pathogens whose taxonomic classification has remained uncertain since 1931. This study used phylogenetic analysis of ribosomal DNA sequences (18S, 28S, 5.8S) and protein-coding genes (actin and β-tubulin) from a Helicosporidium sp. isolated from the blackfly Simulium jonesi to determine its evolutionary position. Genomic DNA was extracted from gradient-purified cysts, amplified by PCR, and sequenced. Comparative analysis using neighbor-joining and maximum-parsimony methods consistently placed Helicosporidium sp. among green algae (Chlorophyta), specifically within the class Trebouxiophyceae as a relative of the achlorophyllous algae Prototheca wickerhamii and Prototheca zopfii. These conclusions were strongly supported by bootstrap and jackknife analyses. The findings definitively show that Helicosporidium is neither a protozoan nor a fungus, but rather represents the first described algal invertebrate pathogen, warranting its taxonomic reclassification within Chlorophyta, Trebouxiophyceae.
Key findings
- Phylogenetic analysis of 18S, 28S, and 5.8S rDNA sequences, plus actin and β-tubulin genes, consistently places Helicosporidium sp. within the green algae (Chlorophyta), not among protozoa or fungi as previously classified
- Helicosporidium sp. clusters as a member of the class Trebouxiophyceae, closely related to the pathogenic achlorophyllous algae Prototheca zopfii and Prototheca wickerhamii
- All phylogenetic trees using different methods (neighbor-joining and maximum-parsimony) supported these relationships with significant bootstrap and jackknife values
- Helicosporidium represents the first described algal entomopathogen, an invertebrate-pathogenic alga that should be reclassified within Chlorophyta rather than remaining in uncertain taxonomic status
This summary was generated automatically from the article PDF and is not part of the original publication. Refer to the PDF for the authoritative text.
Abstract
Historically, the invertebrate pathogens of the genus Helicosporidium were considered to be either protozoa or fungi, but the taxonomic position of this group has not been considered since 1931. Recently, a Helicosporidium sp., isolated from the blackfly Simulium jonesi Stone & Snoddy (Diptera: Simuliidae), has been amplified in the heterologous host Helicoverpa zea. Genomic DNA has been extracted from gradient-purified cysts. The 18S, 28S and 5.8S regions of the Helicosporidium rDNA, as well as partial sequences of the actin and beta-tubulin genes, were amplified by PCR and sequenced. Comparative analysis of these nucleotide sequences was performed using neighbour-joining and maximum-parsimony methods. All inferred phylogenetic trees placed Helicosporidium sp. among the green algae (Chlorophyta), and this association was supported by bootstrap and parsimony jackknife values. Phylogenetic analysis focused on the green algae depicted Helicosporidium sp. as a close relative of Prototheca wickerhamii and Prototheca zopfii (Chlorophyta, Trebouxiophyceae), two achlorophylous, pathogenic green algae. On the basis of this phylogenetic analysis, Helicosporidium sp. is clearly neither a protist nor a fungus, but appears to be the first described algal invertebrate pathogen. These conclusions lead us to propose the transfer of the genus Helicosporidium to Chlorophyta, Trebouxiophyceae.