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Title: MUTATION IN AN RPIAHOMOLOGUE IN ENTEROBACTER CLOACAE AFFECTS CUCUMBER SEED COLONIZATION AND BIOCONTROL OF DAMPING OFF ON CUCUMBER CAUSED BY PYTHIUM ULTIMUM

Author
item Lohrke, Scott
item Dery, Pierre
item REEDY, RALPH - RUTGERS UNIVERSITY
item KOBAYASHI, DONALD - RUTGERS UNIVERSITY
item Roberts, Daniel

Submitted to: Molecular Plant Microbe Interactions
Publication Type: Abstract Only
Publication Acceptance Date: 7/10/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Strains of Enterobacter cloacae have previously been shown to be effective agents for biocontrol of Pythium ultimum induced damping-off on cucumber. However, the exact mechanism(s) responsible for this disease suppression remains unclear. We carried out transposon mutagenesis of wild type Enterobacter cloacae strain 501R3 and screened for mutants reduced in biocontrol of Pythium ultimum induced damping off on cucumber. Strain A145, containing a single mini Tn5-Km insertion, was reduced in disease suppression. In addition to the observed defect in biocontrol, A145 was shown to be reduced in colonization of corn, cowpea, cucumber, sunflower and wheat seeds and also lost the ability to grow on minimal media. Screening of a wild type cosmid library in A145 identified cosmid pECL830, which complemented all three of these phenotypes. Subcloning revealed that a 3.5 Kb KpnI fragment was sufficient for complementation. To identify the exact insertion site, we sequenced pT145, which contains a 3.5 Kb ClaI fragment from A145 containing mini Tn5-Km plus flanking E. cloacae DNA, using primers specific for the ends of mini Tn5-Km. Sequence analysis revealed that the site of insertion was in a region contained on the 3.5 Kb KpnI fragment with a high degree of sequence homology to rpiA, which encodes ribose 5-phosphate isomerase in E. coli. This enzyme in E. coli is involved in the catabolism of ribose 5-phosphate through interconversion with ribulose 5-phosphate. In addition, ribose 5-phosphate is an important metabolic intermediate in the biosynthesis of nucleotides, histidine, tryptophan and cell wall heptoses.