1887

Abstract

The Helicosporidia are invertebrate pathogens that have recently been identified as non-photosynthetic green algae (Chlorophyta). In order to confirm the algal nature of the genus , the presence of a retained chloroplast genome in Helicosporidia cells was investigated. Fragments homologous to plastid 16S rRNA () genes were amplified successfully from cellular DNA extracted from two different isolates. The fragment sequences are 1269 and 1266 bp long, are very AT-rich (60·7 %) and are similar to homologous genes sequenced from non-photosynthetic green algae. Maximum-parsimony, maximum-likelihood and neighbour-joining methods were used to infer phylogenetic trees from an sequence alignment. All trees depicted the Helicosporidia as sister taxa to the non-photosynthetic, pathogenic alga . Moreover, the trees identified spp. as members of a clade that included the heterotrophic species spp. and the mesotrophic species . The clade is always strongly supported by bootstrap values, suggesting that all these organisms share a most recent common ancestor. Phylogenetic analyses inferred from plastid 16S rRNA genes confirmed that the Helicosporidia are non-photosynthetic green algae, close relatives of the genus (Chlorophyta, Trebouxiophyceae). Such phylogenetic affinities suggest that spp. are likely to possess -like organelles and organelle genomes.

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2003-11-01
2019-10-20
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