The coccoid algae (a.k.a "little green balls") are important
primary producers in freshwater communities, but very little is known
about their diversity. This lack of knowledge results from the
extremely small size and simple morphology of these organisms, which
makes identification by light microscopy essentially impossible.
However, molecular techniques allow differentiation of taxa at various
levels and can ultimately lead to species identification. We have
isolated several hundred cultures of coccoid algae from lakes and
ponds in Itasca State Park in northwestern Minnesota and Arrowwood
National Wildlife Refuge in central North Dakota. Many of these
isolates have been examined by light microscopy, 18S rDNA PCR-RFLP
analysis, and 18S rDNA sequence analysis. In addition, some taxa with
multiple isolates have been examined by rbcL and ribosomal RNA
ITS sequence analysis. Our results indicate a high level of diversity,
including possible new species of Chlorella, Muriella,
Pseudomuriella and Mychonastes, among others. We will
discuss the results of our analyses, including implications for
identification of taxa and higher-level systematics. Supported by
National Science Foundation grants DBI-00703867, MCB-0084188 and
DEB-0128952.
Key words: 18S rDNA, Chlorella, Coccoid algae, diversity, Mychonastes