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Journal of Bacteriology, April 2008, p. 2368-2378, Vol. 190, No. 7
0021-9193/08/$08.00+0     doi:10.1128/JB.01495-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

The Iron Stimulon of Xylella fastidiosa Includes Genes for Type IV Pilus and Colicin V-Like Bacteriocins ^,

Paulo A. Zaini,¹ Andréa C. Fogaça,¹ Fernanda G. N. Lupo,¹ Helder I. Nakaya,¹ Ricardo Z. N. Vêncio,^2, and Aline M. da Silva^1*

Departamento de Bioquímica, Instituto de Química,¹ Programa de Pós-Graduação Interunidades em Bioinformática, Universidade de São Paulo, São Paulo, Brazil²

Received 17 September 2007/ Accepted 8 January 2008

Xylella fastidiosa is the etiologic agent of a wide range of plant diseases, including citrus variegated chlorosis (CVC), a major threat to citrus industry. The genomes of several strains of this phytopathogen were completely sequenced, enabling large-scale functional studies. DNA microarrays representing 2,608 (91.6%) coding sequences (CDS) of X. fastidiosa CVC strain 9a5c were used to investigate transcript levels during growth with different iron availabilities. When treated with the iron chelator 2,2'-dipyridyl, 193 CDS were considered up-regulated and 216 were considered down-regulated. Upon incubation with 100 µM ferric pyrophosphate, 218 and 256 CDS were considered up- and down-regulated, respectively. Differential expression for a subset of 44 CDS was further evaluated by reverse transcription-quantitative PCR. Several CDS involved with regulatory functions, pathogenicity, and cell structure were modulated under both conditions assayed, suggesting that major changes in cell architecture and metabolism occur when X. fastidiosa cells are exposed to extreme variations in iron concentration. Interestingly, the modulated CDS include those related to colicin V-like bacteriocin synthesis and secretion and to functions of pili/fimbriae. We also investigated the contribution of the ferric uptake regulator Fur to the iron stimulon of X. fastidiosa. The promoter regions of the strain 9a5c genome were screened for putative Fur boxes, and candidates were analyzed by electrophoretic mobility shift assays. Taken together, our data support the hypothesis that Fur is not solely responsible for the modulation of the iron stimulon of X. fastidiosa, and they present novel evidence for iron regulation of pathogenicity determinants.

Published ahead of print on 25 January 2008.

Supplemental material for this article may be found at http://jb.asm.org/.

Present address: Institute for Systems Biology, 1441 North 34th Street, Seattle, WA 98103-8904.