photo Susan  B.  Barnum , Professor
Miami University: Department of Botany
388 Pearson
Oxford , OH , 45056 United States
(513) 529-4254


(1983) Iowa State University

Areas of Expertise

Evolution of nitrogen fixation genes in cyanobacteria, development of nitrogen fixing anaerobic cells (heterocysts) in cyanobacteria; molecular mechanisms involved in the establishment of symbiosis in cyanobacteria and plants

Research Interests

Cyanobacteria are a diverse group of oxygenic, photosynthetic bacteria that inhabit virtually every major aquatic and terrestrial biome. They have played important evolutionary and ecological roles on Earth. Cyanobacteria have an ancient history dating back at least 3.5 billion years. They diversified to become some of the most successful and ecologically significant organisms on Earth, with respect to longevity and impact on the Earth’s early environment. It is widely believed that caynobacteria were responsible for the conversion of the Earth’s early anaerobic atmosphere to an aerobic one through oxygenic photosynthesis - a pivotal event that led to the evolution of diverse life on Earth. Ancient cyanobacteria also were the progenitors of modern day chloroplasts of plants.

Many cyanobacteria are major suppliers of fixed nitrogen through the process of nitrogen fixation and play important roles in the oceans and in nutrient-depleted regions. While carbon fixation, through photosynthesis, arose early in the evolution of organisms, it is not known when nitrogen fixation first occurred. Two conflicting hypotheses have been proposed: 1) that nitrogen fixation genes are ancient and that the primary nitrogen fixation enzyme, nitrogenase, had a different function originally (detoxification) and 2) that nitrogen fixation is a more recent acquisition. Cyanobacteria exist primarily as free-living bacteria, although some form symbiotic associations with a variety of other organisms.

The overall goals in my laboratory are: 1) to study the evolution of nitrogen fixation genes in bacteria; 2) to study the variation, evolution, excision, and function of insertion elements in cyanobacteria that are excised from within specific genes during heterocyst differentiation and subsequent nitrogen fixation; and 3) to study the molecular interactions of cyanobacterial-plant symbioses.

My students use molecular biology, phylogenetics, and bioinformatics approaches in their research. They use a variety of methods such as PCR, DNA sequencing, microarray analysis, computational analyses using bioinformatics tools to compare sequences, identify functional regions of DNA, and generate phylogenetic trees. We work closely with the Center for Bioinformatics and Functional Genomics.

Selected Publications

Henson, B.J., L.E. Pennington, L.E. Watson, and S.R. Barnum. 2007. Excision of the nifD element in heterocystous cyanobacteria. Archives of Microbiology.

S. R. Barnum. 2005. Biotechnology, 2nd ed. Brooks/Cole/Thomson Publishing, Belmont, California.

B. Henson, L. E. Watson, and S. R. Barnum. 2005. Characterization of a 4 kb variant of the nifD element inAnabaena sp. Strain ATCC 33047.  Current Microbiology 50:129-132.

B. Henson, L. E. Watson, and S. R. Barnum. 2004. The evolutionary history of nitrogen fixation as assessed by nifD.  Journal of Molecular Evolution 58:390-399.

B. Henson, S. M. Hesselbrock, L. E. Watson, and S. R. Barnum. 2004. Molecular phylogeny of the heterocystous cyanobacteria (Subsections IV and V) based on nifD. International Journal of Systematic and Evolutionary Microbiology 54:493-497.

F. Fang and S. R. Barnum. 2004. Expression of the heat shock gene hsp16.6 and promoter analysis in the cyanobacterium Synechocystis sp. PCC 6803. Current Microbiology 49:192-198.

F. Fang and S. R. Barnum. 2003. The heat shock gene, htpG, and thermotolerance in the cyanobacterium, Synechocystis sp. PCC 6803.  Curr. Microbiol. 47:341-346.


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