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Susan R. Barnum
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Research Interests
Cyanobacteria are a diverse group of oxygenic, photosynthetic bacteria that inhabit virtually every major aquatic and terrestrial biome - desert, freshwater and marine, including hot springs and sub-Artic and Antartic regions. Some species are major suppliers of fixed nitrogen through the process of nitrogen fixation and, thus are particularly important in poor soils and nutrient-depleted regions.
Cyanobacteria date back almost 3.5 billion years. They diversified extensively to become some of the most successful and ecologically significant organisms on Earth, with respect to longevity of the lineage and impact on the Earth's early environment. It is widely believed that cyanobacteria were responsible for the conversion of the Earth's anaerobic atmosphere to an aerobic on evia oxygenic photosynthesis - a pivotal event that led to the evolution of diverse life on Earth.
While carbon dioxide fixation, through photosynthesis, arose early in the evolution of organisms, it isnot known when nitrogen fixation first occurred. Since nitrogen fixation is an ancient process that existed before the Earth's atmosphere became aerobic. However, this hypothesis is inconsistent with the random pattern of occurence of nitrogen fixation among various lineages of exant bacteria (including the cyanobacteria), rather than a pattern of universal occurrence that is expected on the basis of an ancient origin.
Our primary objective is to construct a molecular phylogeny of the major lineages of cyanobacteria using ribosomal genes, as an independent framework to evaluate the evolution of nitrogen fixation genes. Three competing hypotheses are being tested:
- nitrogen fixation is ancient and was once universal, but randomly lost;
- nitrogen fixation was acquired by lateral transfer of genes, rather than through vertical, ancestral descent; and
- nitrogen fixation had more than one independent origin.
Understanding these phenomena is essential to understanding the evolution of nitrogen fixation within the cyanobacteria, and should ultimately provide insight into its seemingly haphazard pattern of occurrence within other bacterial lineages.
Selected References
- Barnum, S.R. 1998. Biotechnology: An introduction, Wadsworth Publishing, California. (Book)
- S. Lee, D.J. Prochaska, F. Fang, and S.R. Barnum. 1998. A 16.6 kDa protein in the cyanobacterium, Snynechocystis sp. PCC 6803 plays a role in the heat shock response. Curr. Microbio. 37:403-407.
- Blondin, P. A., Kirby, R. J., and Barnum, S.R. 1993. The heat shock response and acquired thermotolerance in three strains of cyanobacteria. Curr. Microbiol. 26:79-84.
- Perkins, D. R. and Barnum, S. R. 1992. DNA sequence and analysis of a cryptic 4.2 kb plasmid from the filamentous cyano- bacterium, Plactonema sp. Strain PCC 6402. Plasmid 28:170-176.
- Clough, R. C., Matthis, A. L., Barnum, S. R., and Jaworski, J. G. 1992. Purification and characterization of 3-ketoacylacyl carrier protein synthase III from spinach. J. Biol. Chem. 267:20992-20998.
- Froehlich, J., Poorman, R., Reardon, E., Barnum, S. and Jaworski, J. G. 1990. Purification and characterization of acyl carrier protein from two cyanobacteria species. Eur. J. Biochem. 193:817-825.
- Smoker, J. A., Owen, H. A., and Barnum, S. R. 1990. Localization of proteins in filamentous cyanobacteria using immunogold electron microscopy. Meth. Mol. Cell Biol. 2:59-65.
- Smoker, J. A., Owen, H. A., and Barnum, S. R. 1990. Immunolocalization of Rubisco in the nitrogen fixing cyanobacterium, Plectonema boryanum. Protoplasma 156:113-116.
- Smoker, J. A. and Barnum, S. R. 1990. Nitrogenase activity in a filamentous, nonhterocystous cyanobacterium. Arch. Microbiol. 153:417-421.
- Smoker, J. A., Lehmen, L., Owen, H. A., and Barnum, S.R. 1989. Ultrastructure of the nitrogen fixing filamentous, nonheterocystous cyanobacterium, Plectonema boryanum. Protoplasma 152:130-135.
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