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Appl Environ Microbiol. 1986 March; 51(3): 477-480
Copyright © 1986, American Society for Microbiology. All Rights Reserved.

Restriction Endonuclease and nif Homology Patterns of Bradyrhizobium japonicum USDA 110 Derivatives With and Without Nitrogen Fixation Competence

James N. Mathis, L. David Kuykendall and Gerald H. Elkan^*

² Department of Microbiology, North Carolina State University, Raleigh, North Carolina 27695-7615, ¹ and Nitrogen Fixation and Soybean Genetics Laboratory, Plant Physiology Institute, Beltsville Agricultural Research Center, Agricultural Research Service, Beltsville, Maryland 20705²

ABSTRACT

DNAs from Bradyrhizobium japonicum USDA 110 derivatives that differ in nitrogen-fixing ability produced similar electrophoretic patterns with five different restriction enzymes. Our data support the hypothesis of common ancestry for these derivatives. Derivatives I-110 and L1-110 differed as much as 100-fold in acetylene reduction activity when they were tested with several soybean cultivars in both greenhouse and field experiments. While possessing nodulating ability, derivative L1-110 is deficient in symbiotic nitrogen-fixing ability, whereas derivative I-110 is symbiotically competent. Hybridization of nifDK and nifH probes from B. japonicum to Southern blots of restricted DNAs from strain USDA 110 derivatives produced similar patterns. This finding indicates similar structural gene organization for both derivative I-110 and derivative L1-110 and implies that the difference in symbiotic nitrogen fixation is probably not due to structural gene rearrangements. However, our hybridization data do not rule out the possibility of differences in expression of structural nif genes or alterations in the structure or expression of other genes required for symbiotic nitrogen fixation.

^* Corresponding author.

Present address: U.S. Department of Agriculture Agricultural Research Service and Department of Crop Science, North Carolina State University, Raleigh, NC 27695-7631.

Paper 9695 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh.