Anabaena: Difference between revisions
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<br /> It is commonly accepted that cyanobacteria played a key role in the manufacturing of oxygen during the Precambrian period of earth's history. They perform oxygenic photosynthesis, very similar to that of eukaryotic plants and algae, by utilizing water as a reductant source, consequently producing molecular oxygen. Heterocysts, mentioned above, are terminally differentiated cells that specialize in nitrogen fixation. It is believed that the capacity for developing heterocysts first developed when the concentration of oxygen in the atmosphere (largely produced by cyanobacteria) reached levels high enough to cause the inactivation of the nitrogen-fixing enzyme nitrogenase.<font size="+1">'''<br />'''</font><br /> The mechanism of cellular differentiation, or the gene that initiates heterocyst formation has been the focus of much research. To date researchers have found two genes that control both the initiation of heterocyst formation and the frequency of differentiated cells. The product of the ''hetR'' gene is required for heterocyst differentiation and is only transcribed in differentiating cells. The ''patS'' gene regulates the frequency at which cells develop into heterocysts, or essentially inhibits heterocyst formation. The two genes work very differently as evidenced when studying cells carrying mutant genotypes. Cells with mutant ''hetR'' genes do not differentiate at all, where as cells with mutant ''patS'' genes differentiate too often. Conversely, cells that carry extra copies of the ''hetR'' gene differentiate additional heterocysts, and cells with extra copies of the ''patS'' gene do not differentiate at all. {| width="100%" | <br /> It is commonly accepted that cyanobacteria played a key role in the manufacturing of oxygen during the Precambrian period of earth's history. They perform oxygenic photosynthesis, very similar to that of eukaryotic plants and algae, by utilizing water as a reductant source, consequently producing molecular oxygen. Heterocysts, mentioned above, are terminally differentiated cells that specialize in nitrogen fixation. It is believed that the capacity for developing heterocysts first developed when the concentration of oxygen in the atmosphere (largely produced by cyanobacteria) reached levels high enough to cause the inactivation of the nitrogen-fixing enzyme nitrogenase.<font size="+1">'''<br />'''</font><br /> The mechanism of cellular differentiation, or the gene that initiates heterocyst formation has been the focus of much research. To date researchers have found two genes that control both the initiation of heterocyst formation and the frequency of differentiated cells. The product of the ''hetR'' gene is required for heterocyst differentiation and is only transcribed in differentiating cells. The ''patS'' gene regulates the frequency at which cells develop into heterocysts, or essentially inhibits heterocyst formation. The two genes work very differently as evidenced when studying cells carrying mutant genotypes. Cells with mutant ''hetR'' genes do not differentiate at all, where as cells with mutant ''patS'' genes differentiate too often. Conversely, cells that carry extra copies of the ''hetR'' gene differentiate additional heterocysts, and cells with extra copies of the ''patS'' gene do not differentiate at all. {| width="100%" | ||
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<div align="center">'''Figure A''' shows normal ''Anabaena'' grown in a complete medium. '''Figure B''' shows normal ''Anabaena'' growing in a medium lacking nitrogen, arrows indicate heterocysts. '''Figure C''' shows an overexpression of the ''patS'' gene, which inhibits heterocyst formation even in nitrogen-depleted conditions. '''Figure D''' shows the deletion of the ''patS'' gene resulting in the differentiation of additional heterocysts, arrows and brackets indicate heterocysts. <br /> From [http://biocourse.bio.tamu.edu/faculty/jgolden/ Texas A&M University]</div> | <div align="center">'''Figure A''' shows normal ''Anabaena'' grown in a complete medium. '''Figure B''' shows normal ''Anabaena'' growing in a medium lacking nitrogen, arrows indicate heterocysts. '''Figure C''' shows an overexpression of the ''patS'' gene, which inhibits heterocyst formation even in nitrogen-depleted conditions. '''Figure D''' shows the deletion of the ''patS'' gene resulting in the differentiation of additional heterocysts, arrows and brackets indicate heterocysts. <br /> From [http://biocourse.bio.tamu.edu/faculty/jgolden/ Texas A&M University]</div> |
Revision as of 19:03, 31 May 2006
Anabaena flos-aquae f. flos-aquae. From the Microbial Culture Collection
Anabaena oumiana. From the Anabaena Microbial Culture Collection
Classification
Higher order taxa:Bacteria; Cyanobacteria; Nostocales; Nostocaceae; Anabaena Species:Anabaena sp. PCC 7120, Anabaena flos-aque, Anabaena aequalis Description and Significance
Genome Structure
Cell Structure and Metabolism
Ecology
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Figure A shows normal Anabaena grown in a complete medium. Figure B shows normal Anabaena growing in a medium lacking nitrogen, arrows indicate heterocysts. Figure C shows an overexpression of the patS gene, which inhibits heterocyst formation even in nitrogen-depleted conditions. Figure D shows the deletion of the patS gene resulting in the differentiation of additional heterocysts, arrows and brackets indicate heterocysts.
From Texas A&M University |
References
Updated May 31, 2006
Cyanobase: Anabaena sp. PCC 7120
ExPaSy Molecular Biology Server: Heterocyst or not Heterocyst?
Kenyon College: Heterocyst formation in Anabaena and other cyanobacteria
Microbiology and Molecular Biology Reviews: Nitrogenase
University of Chicago: How Cyanobacteria Count to 10