| AN1/12-5, acoccoid eustigmatophyte |  |
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.JL2-5, a coccoid trebouxiophyte. |
Coccoid algae
Research in the Department of Biological Sciences, North Dakota State University
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What are coccoid algae? To phycologists, coccoid is a level of organization, or general form of the organism. Most textbooks refer to the coccoid level of organization as organisms that are unicellular, non-flagellate and surrounded by a cell wall or other firm covering. The definition for coccoid in dictionaries is different, referring to a spherical shape. In our work, we use this more limited definition so that coccoid algae are those algae that are non-flagellate, unicellular, and roughly spherical in shape. The coccoid algae pictured are only about 5-6 µm maximum diameter.
Coccoid organisms can be found in several different groups of algae, including the Chlorophyta (green algae), Chrysophyceae (golden-brown algae), Xanthophyceae (yellow-green algae), to name only a few. Most coccoid algae are small and the combination of their size and very simple morphology makes them very difficult to identify. Some coccoid algae produce flagellate cells (zoospores) for asexual reproduction. These are the zoosporic coccoids. Others asexually reproduce by making new, small coccoid cells (autospores) inside the old cell wall. These are the autosporic coccoids. A few coccoid algae reproduce only by simple cell division.
Our research has focused on the autosporic coccoids that are green in color for two reasons. First, we found an abundance of green autosporic coccoid algae at some of our study sites, and we wanted to find out what they are. Second, the lack of any flagellate cell makes them extremely difficult to characterize and identify, so we needed to develop new identification criteria based on molecular methods. We have focused on algae cultured from a series of lakes in the Arrowwood National Wildlife Refuge, ND. These shallow lakes were formed by impounding the James River. Additional research is focusing on coccoid algae from Itasca State Park, Minnesota.
Here's how we are identifying green autosporic coccoid algae.
In our Itasca study, we are working with over 200 isolates of coccoid algae. In order to efficiently identify these isolates, we use a relatively simple procedure call PCR-RFLP targeting the 18S rDNA. To determine genetic identity, we perform PCR-RFLP of the 18S rDNA with specific restriction enzymes, primarily HaeIII and TaqI. These enzymes cut PCR-amplified 18S rDNA of coccoid algae at several sites, producing multiple fragments.
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The gel pictured here shows the
HaeIII PCR-RFLP of
the 18S rDNA of three trebouxiophyte isolates, JL2-2, JL2-5 and JL2-7. The
patterns of fragments are all different, indicating that the sequences of
the 18S rDNA are different.
Although somewhat controversial, our analysis indicates that if isolates have different 18S rDNA PCR-RFLP patterns, then they are different species. Thus, the three isolates, JL2-2, JL2-5, and JL2-7 are all different species of autosporic coccoid trebouxiophytes. |
By comparing the size of the fragments produced by PCR-RFLP to the published sequences of the 18S rDNA of coccoid algae, we can determine the species of an isolate. However, almost all of our isolates do not match any sequenced organism. They are probably previously undescribed species.
Additional research is focusing on sequence analysis of the 18S rDNA of our isolates. In addition, each isolate is being examined by light microscopy and unique types are being examined by electron microscopy and HPLC to determine photosynthetic pigments. We are also examining the 18S-26S ITS region of multiple isolates with identical 18S PCR-RFLP fragments to find additional diversity. As new information becomes available from these analyses, the corresponding pages will be updated.
To see our data from the Arrowwood study, go on to our Arrowwood results page.
To see the results from our Itasca Study, go on to our Itasca results page.
This material is based upon work supported by the National Science Foundation under grants DEB-9707262, MCB-0084188, DBI-0070387 and OSR-9452892. Additional support was provided by the North Dakota Water Resources Research Institute. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.