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Journal of Bacteriology, November 2000, p. 6233-6238, Vol. 182, No. 21
Istituto di Microbiologia, Università
di Roma "La Sapienza",1 Dipartimento
di Biologia, Università di Roma Tre,2 and
Unità di Microbiologia Molecolare, I.R.C.C.S. "Lazzaro
Spallanzani",3 00100 Rome, Italy
Received 27 March 2000/Accepted 1 August 2000
PseudobactinB10, the fluorescent siderophore produced
by the rhizobacterium Pseudomonas strain B10, contains the
hydroxamate ligand
D-N5-hydroxyornithine
(D-N5-OH-Orn). We cloned the
L-Orn N5-oxygenase
(psbA) gene from a genomic library of
Pseudomonas strain B10 and demonstrated that PsbA is
involved in the conversion of L-Orn to its
N5-OH derivative. PsbA shows significant
similarity to microbial
0021-9193/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Pseudobactin Biogenesis in the Plant Growth-Promoting
Rhizobacterium Pseudomonas Strain B10: Identification
and Functional Analysis of the L-Ornithine
N5-Oxygenase (psbA) Gene
-amino acid hydroxylases containing flavin
adenine dinucleotide and NADP cofactor-binding sites and the FATGY
signature of the putative substrate recognition pocket. The
psbA gene is monocistronic, and its transcription is
negatively controlled by iron. A site-specific psbA mutant
of Pseudomonas strain B10 was biochemically complemented with the precursor L-N5-OH-Orn,
suggesting that L-Orn is hydroxylated before conversion to
the D isomer. The L-Orn
N5-hydroxylase-defective mutants of
Pseudomonas strain B10 and Pseudomonas aeruginosa PAO1 were much less effective than the parental
strains in suppressing the growth of the phytopathogen Erwinia
carotovora in iron-poor medium. The extent of in vitro inhibition
of E. carotovora was strictly iron dependent and directly
correlated with the amount of released siderophores. These data
strengthen the role of fluorescent siderophores in biocontrol of
deleterious rhizomicroorganisms.
*
Corresponding author. Mailing address: Dipartimento di
Biologia, Università di Roma Tre, Viale G. Marconi 446, 00146 Rome, Italy. Phone: 39.6.5517.6331. Fax: 39.6.5517.6321. E-mail:
visca{at}bio.uniroma3.it.
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