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Applied and Environmental Microbiology, June 2008, p. 3652-3657, Vol. 74, No. 12
0099-2240/08/$08.00+0     doi:10.1128/AEM.02386-07
Copyright © 2008, American Society for Microbiology. All Rights Reserved.

Hypervariations of a Protease-Encoding Gene, PD0218 (pspB), in Xylella fastidiosa Strains Causing Almond Leaf Scorch and Pierce's Disease in California

USDA-ARS, Parlier, San Joaquin Valley Agricultural Sciences Center, 9611 S. Riverbend Avenue, Parlier, California 93648,¹ USDA-APHIS, Center for Plant Health Science and Technology, Pest Epidemiology and Risk Assessment Laboratory, 1730 Varsity Drive, Suite 300, Raleigh, North Carolina 27606,² Department of Plant Pathology, University of California, Davis, California 95616,³ Paramount Farming Co., 33141 E. Lerdo Highway, Bakersfield, California 93308⁴

Received 23 October 2007/ Accepted 10 April 2008

Xylella fastidiosa is a gram-negative plant pathogenic bacterium that causes almond leaf scorch disease (ALSD) and Pierce's disease (PD) of grape in many regions of North America and Mexico. Of the two 16S rRNA gene genotypes described in California, A genotype strains cause ALSD only and G genotype strains cause both PD and ALSD. While G genotype strains cause two different diseases, little is known about their genetic variation. In this study, we identified a putative protease locus, PD0218 (pspB), in the genome of X. fastidiosa and evaluated the variation at this locus in X. fastidiosa populations. PD0218 contains tandem repeats of ACDCCA, translated to threonine and proline (TP), upstream of the putative protease conserved domain. Among 116 X. fastidiosa ALSD and PD strains isolated from seven locations in California, tandem repeat numbers (TRNs) varied from 9 to 47, with a total of 30 TRN genotypes, indicating that X. fastidiosa possesses an active mechanism for contracting and expanding tandem repeats at this locus. Significant TRN variation was found among PD strains (mean = 29.9), which could be further divided into two TRN groups: PD-G_small (mean = 17.3) and PD-G_large (mean = 44.3). Less variation was found in ALSD strains (mean = 21.7). The variation was even smaller after ALSD strains were subdivided into the A and G genotypes (mean = 13.3, for the G genotype; mean = 27.1, for the A genotype). Genetic variation at the PD0218 locus is potentially useful for sensitive discrimination of X. fastidiosa strains. However, TRN stability, variation range, and correlation to phenotypes should be evaluated in epidemiological applications such as pathotype identification and delineation of pathogen origin.

Published ahead of print on 2 May 2008.