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Applied and Environmental Microbiology, July 2000, p. 2764-2772, Vol. 66, No. 7
Department of Plant Pathology, University of
California, Riverside, California 92521-0122
Received 1 November 1999/Accepted 10 April 2000
In vivo expression technology (IVET) was employed to study
colonization of Phytophthora parasitica by a biological
control bacterium, Pseudomonas putida 06909, based on a new
selection marker. The pyrB gene, which encodes aspartate
transcarbamoylase, an enzyme used for pyrimidine biosynthesis, was
cloned from P. putida 06909. A pyrB-disrupted
mutant did not grow in pyrimidine-deficient media unless it was
complemented with pyrBC' behind an active promoter. Thirty
clones obtained from P. putida 06909 that were expressed on
fungal hyphae but not on culture media were isolated by IVET based on
the promoterless transcriptional fusion between pyrBC' and
lacZ. Nineteen of these clones were induced during late-stage bacterial growth in vitro, while 11 of the clones were expressed only when they were inoculated onto fungal hyphae.
Restriction analysis of these 11 clones revealed that there were five
unique clones. Sequence analyses of three of the five unique clones
showed that the 3' ends of the clones fused to pyrB were
similar to genes encoding diacylglycerol kinase (DAGK), bacterial ABC
transporters, and outer membrane porins. The sequences of the two other
clones were not similar to the sequences of any of the genes in the
database used. A LuxR family response regulator was found upstream of
DAGK, and a LysR family response regulator was found upstream of the ABC transporter. The location of the inducible promoter of two clones
suggested that DAGK and the ABC transporter are induced and may play a
role in colonization of the fungus P. parasitica by
P. putida 06909.
0099-2240/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Genes Expressed in Pseudomonas putida
during Colonization of a Plant-Pathogenic Fungus
*
Corresponding author. Mailing address: Department of
Plant Pathology, University of California, Riverside, CA 92521-0122. Phone: (909) 787-3516. Fax: (909) 787-4294. E-mail:
Cooksey{at}citrus.ucr.edu.
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