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ARS Home » Research » Publications at this Location » Publication #128077
Title: MUTATION IN RPIA HOMOLOGUE IN ENTEROBACTER CLOACAE DECREASES COLONIZATION AND BIOCONTROL OF DAMPING-OFF BY PYTHIUM ULTIMUM

Author
item Lohrke, Scott
item DERY, PIERRE - FORMER USDA
item LI, W - HUBEI UNIV, PR CHINA
item REEDY, R - RUTGERS, PLANT PATHOLOGY
item KOBAYASHI, D - RUTGERS, PLANT PATHOLOGY
item Roberts, Daniel

Submitted to: Molecular Plant Microbe Interactions
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/7/2002
Publication Date: N/A
Citation: N/A

Interpretive Summary: Soilborne plant pathogens cause diseases that result in major economic losses to farmers in the United States. Biological control of plant diseases is an environmentally friendly and promising alternative to the use of chemicals for control of these important soilborne plant pathogens. Biological control can be inconsistent and this inconsistency in performance is hampering widespread commercial application of biocontrol agents. One factor contributing to this inconsistency is poor colonization of plant roots by biocontrol agents. The rpiA gene, which encodes the enzyme ribose phosphate isomerase, was cloned, sequenced, and shown to be of major importance to colonization of roots of diverse crop plants by the potential biocontrol bacterium Enterobacter cloacae. This information will be useful to scientists. Knowledge of the genetic and physiological basis of colonization of plant roots by biocontrol agents will enable scientists to devise strategies to enhance colonization and biological control performance.

Technical Abstract: Strains of Enterobacter cloacae show promise as biocontrol agents for Pythium ultimum induced damping-off on cucumber and other crops. E. cloacae A145 is a mini-Tn5 Km transposon mutant of strain 501R3 that was significantly reduced in suppression of damping-off on cucumber caused by P. ultimum. Strain A145 was deficient in colonization of cucumber, sunflower, and wheat seeds and significantly reduced in colonization of corn and cowpea seeds relative to strain 501R3. Populations of strain A145 were also significantly lower than those of strain 501R3 at all sampling times in cucumber, wheat, and sunflower rhizosphere. Populations of strain A145 were not detectable in any rhizosphere after 42 days while populations of strain 501R3 remained at substantial levels throughout all experiments. Molecular characterization of strain A145 indicated mini-Tn5 Km was was inserted in a region of the E. cloacae genome with a high degree of DNA Aand amino acid sequence similarity to rpiA, which encodes ribose-5- phosphate isomerase. In E. coli, RpiA catalyzes the interconversion of ribose-5-phosphate and ribulose-5-phosphate and is a key enzyme in the pentose phosphate pathway. Ribose-5-phosphate isomerase activity in cell lysates from strain A145 was approximately 3.5% that from strain 501R3. In addition, strain A145 was a ribose auxotroph, as expected for an rpiA mutant. Introduction of a 1.0-kb DNA fragment, containing only the rpiA homologue, into strain A145 genetically restored ribose phosphate isomerase activity, prototrophy, seed colonization, and disease suppression to levels similar to those associated with strain 501R3. Experiments reported here indicate a key role for rpiA, and possibly the pentose phosphate pathway, in suppression of damping-off and colonization of plants by E. cloacae.