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United States Department of Agriculture

Agricultural Research Service

Title: A Xanthomonadin-Encoding Gene Cluster for the Identification of Pathovars of Xanthomonas Campestris

Authors
item Poplawsky A R, - UNIV. OF IDAHO
item Kawalek M D, - UNIV. CALIF. RIVERSIDE
item Schaad, Norman

Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 1, 1993
Publication Date: N/A

Interpretive Summary: Xanthomonads are the most common and numerous group of plant pathogenic bacteria. The genus contains 120 different pathogens. The most useful diagnostic character to identify a species of Xanthomonas is a species specific yellow pigment called xanthomonadin. The pigment is easily produced by colonies growing on agar medium, however, many other non- pathogenic bacteria produce a different yellow pigment which is usually difficult to distinguish from xanthomonadin. The pigment can be differentiated only by expensive chromatography assays. The purpose of this work was to determine if a simple genetic probe could be developed and used for rapid identification of xanthomonads. Results showed that a segment of the xanthomonadin gene was indeed specific and could be used as a probe to distinguish pathovars of Xanthomonas campestris from other species of bacteria associated with plants

Technical Abstract: A gene cluster for xanthomonadin pigment production was obtained from Xanthomonas campestris pv. campestris, the causal agent of black rot of crucifers. Eighteen mutants affected in pigment production were identified. Seventeen of these mutants were fully pathogenic, and they could be divided into four classes based on the absorption spectra of pigment extracts. Sequences from a 25.4-kbp genomic clone (pIG102) restored pigment production to all 18 mutants and to a naturally occurring nonpigmented strain of X. c. pv. mangiferaeindicae. Analysis of pIG102 by subcloning and mutant restoration identified six functional domains for pigment production, and this genomic region conferred the production of the pigment to Pseudomonas fluorescens. Clone pIG102 hybridized strongly to all strains of 18 pathovars of X. campestris and showed little or no hybridization to 105 strains of Pseudomonas, Erwinia, and Clavibacter. In Southern hybridizations, there was no strict correlation between pathovar designation and the restriction fragment length polymorphism pattern of the pigment-encoding region. A pIG102 subclone, pIG233, hybridized to all of the X. campestris strains but showed no hybridization to the non- xanthomonads. These probes should be useful in distinguishing X. campestris pathovars from other genera of bacteria associated with plants

Last Modified: 12/20/2014
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