Donald L. Keister
	Research Leader, USDA-ARS Soybean and Alfalfa Research Laboratory, Bldg. 006, BARC-West, Beltsville, MD 20705 Tel. 301-504-5723 FAX 301-504-5728 E-mail: dkeister@asrr.arsusda.gov

	INTRODUCTION TO PROJECTS
	How microbes interact with plants is the broad theme of my research. Understanding the factors involved and the mechanism(s) is important for enhancing biological symbiotic nitrogen fixation and controlling pathogen interactions.
	Beta-Glucans in Plant-Microbe Interaction
	My current program focuses on the role of cyclic beta-glucans which are produced by the bacteria in symbiotic interactions with soybean plants. These glucans are composed of 10-14 glucose molecules cyclized with mixed beta-(1,3-) and (1,6-) linkages. The glucans are synthesized in cytoplasm and translocated to the periplasm where they function in osmotic regulation of the periplasmic space of the microbe. They appear to have additional function(s) as well and current work suggests that they may be involved in suppression of the plant defense response during nodule formation by the symbiotic microorganism.
	Role of Cytochrome P450 in Bradyrhizobium japonicum
	Cytochromes P450 are found in plants, animals and microbes and are involved in a variety of oxidative reactions in cells. The function of P450 in (Brady) Rhizobium is not known. We have sequenced a DNA region containing a P450 gene and found a large cluster of genes including three complete P450 genes and five additional open reading frames that appear to be an operon. The open reading frames have similarity to genes in other organizations involved in terpenoid synthesis. It is tempting to speculate that the operon maybe involved in gibberellin synthesis. Work is continuing to identify the biochemical product.
	Competition for Nodulation
	Soil where soybeans have been grown contains an indigenous population of bacteria which nodulate the plants. Many of these bacteria are poor to average in nitrogen fixation. Superior nitrogen-fixing strains exist but introducing them into the soil so that they form a majority of the nodules on the plant has not been successful. We are developing more competitive strains which will enhance symbiotic nitrogen fixation using a combination of molecular and physiological selection procedures. A patent has been applied for on a new competitive strain.

	Representative Publications
	Early career
	Keister, D.L., San Pietro, A. and Stolzenbach, F.E. 1960. Purification and properties of pyridine nucleotide transhydrogenise from spinach. J. Biol.Chem. 235:2989-2996.
	Keister, D.L. and Yike, N.J. 1967. Energy-linked reactions in photosynthetic bacteria. I. Succinate-linked ATP-driven NAD+ reduction by Rhodospirillum rubrum chromatophores. Arch. Biochem. Biophys. 121:415-422, 1967
	Keister, D.L. 1975. Acetylene reduction by pure cultures of rhizobia. J. Bacteriol. 123:1265-1268.
	Recent
	Tully, R.C. and Keister, D.L. 1993. Cloning and mutagenesis of a cytochrome P-450 locus from Bradyrhizobium japonicum that is expressed anaerobically and symbiotically. Appl. Environ. Microbiol. 59:4136-4142.
	Bhagwat, A.A. and Keister, D.L. 1992. Cloning of Bradyrhizobium japonicum genes expressed strain specifically in soil/rhizosphere. Appl. Environ. Microbiol. 58:1490-1495.
	Bhagwat, A.A. and Keister, D.L. 1995. Site-directed mutagenesis of the ß-(1,3)(1,6)-glucan synthesis locus of Bradyrhizobium japonicum. Mol. Plant-Microbe Interact. 8:366-370.
	Dunlap, J., Minami, E., Bhagwat, A.A., Keister, D.L., and Stacey, G. 1996. Nodule development induced by mutants of Bradyrhizobium japonicum defective in cyclic ß-glucan synthesis. Mol. Plant-Microbe Interact. 9:546-555.
	Pfeffer, P.E., Osman, S.F., Hotchkiss, A., Bhagwat, A.A., and Keister, D.L. 1996. Cyclolaminarinose. A new biologically active ß-(1,3)-cyclic glucan. Carbohy. Res. 296:23-37.
	Bhagwat, A.A., Mithöfer, A. and Keister, D.L. 1998. Further studies on the role of cyclic ß-gluvans in symbiosis. A ndvC mutant of Bradyrhizobium japonicum synthesizes cyclodecakis-(1-3)-ß-glucosyl. Plant Physiol., In Press
	Tully, R.E., van Berkum, P., Lovins, K.W. and Keister, D.L. 1998. Identification and sequencing of a cytochrome P450 gene cluster from Bradyrhizobium japonicum. Biochem. Biophys. Acta. 398:243-255.

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