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Applied and Environmental Microbiology, May 2001, p. 2263-2269, Vol. 67, No. 5
Fundo de Defesa da Citricultura
(Fundecitrus), 14807-040, VI. Melhado-C.P. 391, Araraquara, São
Paulo, Brazil,1 and Laboratoire de
Biologie Cellulaire et Moléculaire, I.B.V.M., I.N.R.A. et
Université Victor Segalen Bordeaux 2, 33883 Villenave d'Ornon
Cedex, France2
Received 23 October 2000/Accepted 26 February 2001
Xylella fastidiosa is a gram-negative, xylem-limited
bacterium affecting economically important crops (e.g., grapevine,
citrus, and coffee). The citrus variegated chlorosis (CVC) strain of
X. fastidiosa is the causal agent of this severe disease
of citrus in Brazil and represents the first plant-pathogenic bacterium for which the genome sequence was determined. Plasmids for the CVC
strain of X. fastidiosa were constructed by combining
the chromosomal replication origin (oriC) of X.
fastidiosa with a gene which confers resistance to kanamycin
(Kanr). In plasmid p16KdAori, the oriC
fragment comprised the dnaA gene as well as the two
flanking intergenic regions, whereas in plasmid p16Kori the
oriC fragment was restricted to the
dnaA-dnaN intergenic region, which
contains dnaA-box like sequences and AT-rich clusters.
In plasmid p16K, no oriC sequence was present. In the
three constructs, the promoter region of one of the two X.
fastidiosa rRNA operons was used to drive the transcription of
the Kanr gene to optimize the expression of kanamycin
resistance in X. fastidiosa. Five CVC X.
fastidiosa strains, including strain 9a5c, the genome sequence
of which was determined, and two strains isolated from coffee, were
electroporated with plasmid p16KdAori or p16Kori. Two CVC isolates,
strains J1a12 and B111, yielded kanamycin-resistant transformants when
electroporated with plasmid p16KdAori or p16Kori but not when
electroporated with p16K. Southern blot analyses of total DNA extracted
from the transformants revealed that, in all clones tested, the plasmid
had integrated into the host chromosome at the promoter region of the
rRNA operon by homologous recombination. To our knowledge, this is the
first report of stable transformation in X. fastidiosa.
Integration of oriC plasmids into the X.
fastidiosa chromosome by homologous recombination holds
considerable promise for functional genomics by specific gene inactivation.
0099-2240/01/$04.00+0 DOI: 10.1128/AEM.67.5.2263-2269.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Stable Transformation of the Xylella
fastidiosa Citrus Variegated Chlorosis Strain with
oriC Plasmids
*
Corresponding author. Present address: Fundo de Defesa
da Citricultura (Fundecitrus), Av. Dr. Adhemar Pereira de Barros, 201, 14807-040, VI. Melhado-C.P. 391, Araraquara, São Paulo, Brazil. Phone: (55) 16 201 7025. Fax: (55) 16 201 7032. E-mail:
pbmonteiro@fundecitrus.com.br.
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