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Journal of Bacteriology, January 2000, p. 91-99, Vol. 182, No. 1
Department of Biochemistry and Molecular and
Cellular Biology of Plants, Estación Experimental del
Zaidín, Consejo Superior de Investigaciones
Científicas,1 and GX-Biosystems
España, Pinos Genil,2 Granada, Spain,
and Department of Microbiology, Technical University of
Denmark, Lyngby, Denmark3
Received 15 June 1999/Accepted 11 October 1999
Pseudomonas putida KT2442 is a root-colonizing strain
which can use proline, one of the major components in root exudates, as
its sole carbon and nitrogen source. A P. putida mutant
unable to grow with proline as the sole carbon and nitrogen source was isolated after random mini-Tn5-Km mutagenesis. The
mini-Tn5 insertion was located at the putA
gene, which is adjacent to and divergent from the putP
gene. The putA gene codes for a protein of 1,315 amino acid
residues which is homologous to the PutA protein of Escherichia
coli, Salmonella enterica serovar Typhimurium,
Rhodobacter capsulatus, and several Rhizobium
strains. The central part of P. putida PutA
showed homology to the proline dehydrogenase of Saccharomyces
cerevisiae and Drosophila melanogaster, whereas the
C-terminal end was homologous to the pyrroline-5-carboxylate dehydrogenase of S. cerevisiae and a number of aldehyde
dehydrogenases. This suggests that in P. putida, both
enzymatic steps for proline conversion to glutamic acid are catalyzed
by a single polypeptide. The putP gene was homologous to
the putP genes of several prokaryotic microorganisms, and
its gene product is an integral inner-membrane protein involved in the
uptake of proline. The expression of both genes was induced by proline
added in the culture medium and was regulated by PutA. In a P. putida putA-deficient background, expression of both
putA and putP genes was maximal and proline
independent. Corn root exudates collected during 7 days also strongly
induced the P. putida put genes, as determined by using
fusions of the put promoters to 'lacZ. The
induction ratio for the putA promoter (about 20-fold) was
6-fold higher than the induction ratio for the putP promoter.
0021-9193/0/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Proline Catabolism by Pseudomonas putida: Cloning,
Characterization, and Expression of the put Genes in the
Presence of Root Exudates
*
Corresponding author. Mailing address: Department of
Biochemistry and Molecular and Cellular Biology of Plants,
Estación Experimental del Zaidín, Consejo Superior de
Investigaciones Científicas, Calle Profesor Albareda 1, E-18008
Granada, Spain. Phone: 34-958-121011. Fax: 34-958-129600. E-mail:
jlramos{at}eez.csic.es.
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