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Applied and Environmental Microbiology, June 2001, p. 2641-2648, Vol. 67, No. 6
MSU-DOE Plant Research
Laboratory,1 NSF Center for Microbial
Ecology,2 Genetics
Program,3 and Department of
Microbiology,4 Michigan State
University, East Lansing, Michigan 48824
Received 28 November 2000/Accepted 24 March 2001
The regulation of the nutrient-deprivation-induced
Sinorhizobium meliloti homogentisate dioxygenase
(hmgA) gene, involved in tyrosine degradation, was
examined. hmgA expression was found to be independent of
the canonical nitrogen regulation (ntr) system. To
identify regulators of hmgA, secondary mutagenesis of an
S. meliloti strain harboring a hmgA-luxAB
reporter gene fusion (N4) was carried out using transposon
Tn1721. Two independent Tn1721 insertions
were found to be located in a positive regulatory gene (nitR), encoding a protein sharing amino acid sequence
similarity with proteins of the ArsR family of regulators. NitR was
found to be a regulator of S. meliloti hmgA expression
under nitrogen deprivation conditions, suggesting the presence of a
ntr-independent nitrogen deprivation regulatory system.
nitR insertion mutations were shown not to affect
bacterial growth, nodulation of Medicago sativa
(alfalfa) plants, or symbiotic nitrogen fixation under the
physiological conditions examined. Further analysis of the nitR locus revealed the presence of open reading frames
encoding proteins sharing amino acid sequence similarities with an
ATP-binding phosphonate transport protein (PhnN), as well as
transmembrane efflux proteins.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.6.2641-2648.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
The Sinorhizobium meliloti
Nutrient-Deprivation-Induced Tyrosine Degradation Gene
hmgA Is Controlled by a Novel Member of the
arsR Family of Regulatory Genes
*
Corresponding author. Mailing address: Michigan State
University, Department of Botany and Plant Pathology, Plant Biology Building, Room 366, East Lansing, MI 48824. Phone: (517) 353-9399. Fax:
(517) 353-1926. E-mail: milcamps{at}pilot.msu.edu.
Present address: INRA/CNRS Laboratoire de Biologie Moleculaire de
Relations Plantes-Microorganismes, 31326 Castanet Tolosan Cedex, France.
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