Phylogeny of chlamydomonads isolated from saline habitats: Inferences from 18S and 26S rDNA data

Although the vast majority of chlamydomonadalean organisms are found in freshwater habitats, several prominent lineages (e.g., Dunaliella, Brachiomonas and some species of Chlamydomonas) are found in brackish, marine or brine environments. Unknown chlamydomonads from Salt Plains National Wildlife Refuge (SPMO; OK USA) and from the Culture Collection of Marine Phytoplankton (CCMP; Bigelow Labs, ME USA) were included in a broad phylogenetic analysis using both 18S and 26S rDNA data. Results indicate that several halotolerant/halophilic lineages can be identified among the Chlamydomonadales. One lineage, which includes Chlamydomonas parkeae, Chl. hedleyi (symbiont of foraminifer) and five CCMP isolates, is allied in the Tetracystis clade with Chl. moewusii and Chl. noctigama. A second group, which includes Chl. reginae, Chl. uva-maris and CCMP 233, is allied with Chl. monadina. Brachiomonas, which is sister to Haematococcus lacustris, has no close halotolerant/halophilic allies. The three SPMO isolates plus CCMP 220 and CCMP 1641 are resolved as close allies of various Dunaliella taxa. Two of the SPMO isolates are distinctive from a typical Dunaliella cell in that they regularly form non-flagellated cellular aggregations in normal saline media. In summary, these observations collectively suggest that the ability to live in a saline habitat has arisen, independently, in at least four chlamydomonadalean lineages. In addition, substantial taxonomic revision is required to accommodate virtually all of the unidentified isolates included in this investigation.