David H. Keating, Ph.D.
Assistant Professor

Ph.D., University of Illinois at Urbana-Champaign

Molecular Microbiologist

Mechanisms of communication between bacteria and plants:
 the alfalfa nitrogen-fixing symbiosis

The growth of most plants is dependent on the availability of reduced forms of nitrogen. Members of the Fabacae (legume) family avoid this growth limitation by entering into a symbiotic relationship with bacteria, allowing the plant access to the abundant pool of dinitrogen in the atmosphere. These plants produce structures called root nodules in which differentiated intracellular bacteria convert nitrogen to ammonia in return for plant photosynthates. The symbiosis is highly specific, in that one species of plant interacts with a very limited number of bacteria and is mediated by an exchange of chemical signals between the symbiotic partners.

We use a combination of genomics, bacterial genetics, and biochemistry to better understand the mechanisms of communication between these two organisms. Our work has focused on the carbohydrates that comprise the cell surface of the bacterium Sinorhizobium meliloti. These carbohydrates are decorated by the covalent attachment of sulfate, a modification previously believed to only occur in eukaryotes. We are interested in the role of sulfated carbohydrates as a symbiotic signal, as a tool to understand the structure/function of bacterial cell surface, and as a model for understanding the biochemistry of carbohydrate sulfation in higher organisms.

Selected Publications

D. H. Keating. 2007. Sinorhizobium meliloti SyrA is a Transcriptional Regulator of Genes Involved in LPS Sulfation and Exopolysaccharide Biosynthesis. J. Bacteriol.189:2510-20.

D. H. Keating. 2007. The Sinorhizobium meliloti ExoR Protein Is Required for Transcriptional Downregulation of lpsS Transcription and Succinoglycan Biosynthesis in Response to Divalent Cations. FEMS Microbiol. Lett. 267:23-29.

A. H. Klein, A. Shulla, S. A. Reimann, D. H. Keating and A. J.  Wolfe. 2007. The Intracellular Concentration of Acetyl Phosphate in Escherichia coli Is Sufficient for Direct Phosphorylation of Two-Component Response Regulators.
J Bacteriol. 189:5574-81

Cronan, G. E., Campbell, G. R. O., G. C. Walker, and D. H. Keating. (2006). Diverse Sinorhizobium meliloti Mutants Show Reduced Lipopolysaccharide Sulfation. Submitted. J. Bacteriol.

G. E. Townsend II, and D. H. Keating. (2006). Mesorhizobium loti Produces NodPQ Dependent Sulfated Cell-Surface Polysaccharides. J. Bacteriol. 188:8560-72.

Cronan, G. E. and D. H. Keating. (2004).  Sinorhizobium meliloti Lipopolysaccharide Sulfotransferase. J. Bacteriol. 186:168–4176.  

Keating, D. H., Campbell, G. R. O., and G. C. Walker. (2004) Diverse Sinorhizobium meliloti Mutants Show Reduced Lipopolysaccharide Sulfation. Under revision. J. Bacteriol.

Wais, Rebecca, Keating, David, H. and Long, Sharon R. (2002). Structure Function Analysis of Nod Factor-Induced Root Hair Calcium Spiking in Rhizobium-Legume Symbiosis. Plant Physiol. 129: 211-224.

Keating, David H., Willits, Michael G., and Long, Sharon R. (2002).  A Sinorhizobium meliloti Mutant Altered in Lipopolysaccharide Sulfation Is Defective in Symbiosis. J. Bacteriol. 184:6681-6689.

Galibert, F. et al. (2001). The composite genome of the legume symbiont Sinorhizobium meliloti. Science. 293:668-672.

Barnett, M. J. et al. (2001). Nucleotide sequence and predicted functions of the entire Sinorhizobium meliloti pSymA megaplasmid. Proc Natl Acad Sci. 98:9883-9888.

Search PubMed for a complete listing of David Keating's publications

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