Submitted to: BARC Poster Day
Publication Type: Abstract Only
Publication Acceptance Date: April 25, 2001
Publication Date: N/A
Enterobacter cloacae has previously been shown to be an effective biocontrol agent of Pythium ultimum induced damping-off on cucumber. However, the exact mechanism(s) responsible for disease suppression remains unclear. Transposon mutants of Enterobacter cloacae strain 501R3 were screened for mutants reduced in biocontrol. Strain A145, containing a single mini Tn5-Km insertion, was reduced in disease suppression. Strain A145 was also reduced in colonization of corn, cowpea, cucumber, sunflower and wheat seeds and lost the ability to grow on minimal media. Cosmid pECL830, which contained strain 501R3 DNA, 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 is involved in the catabolism of ribose 5-phosphate. Ribose 5-phosphate is an important metabolic intermediate in the biosynthesis of nucleotides, histidine, tryptophan and cell wall heptoses. Preliminary data indicated that serA and iciA, encoding D-3- phosphoglycerate dehydrogenase and inhibitor of chromosome initiation, respectively, are adjacent to rpiA.