ARS | Publication request: Reduced carbon utilization, competitive colonization of the spermosphere, and disease suppression by Enterobacter cloacae

Submitted to: International Plant Growth Promoting Rhizobacteria Workshop
Publication Type: Abstract Only
Publication Acceptance Date: May 22, 2009
Publication Date: June 1, 2009
Citation: Roberts, D.P., Mckenna, L.F., Buyer, J.S. 2009. Reduced carbon utilization, competitive colonization of the spermosphere, and disease suppression by Enterobacter cloacae [abstract]. International Plant Growth Promoting Rhizobacteria Workshop.

Technical Abstract: De Wit Replacement series and disease suppression experiments with a collection of nutritional mutants of E. cloacae 501R3 are being used to determine the role of reduced carbon compounds found in seed exudate during beneficial activities by this bacterium. Mutants A-11, M2, and M43 contain single mini-Tn5 Km insertions in pfkA, sdhA, and aceF, respectively. A-11 was severely impaired in growth on almost all carbohydrates, M2 was severely impaired in growth on almost all amino acids and organic acids, and M43 was severely impaired in growth on almost all carbohydrates, amino acids, and organic acids detected in cucumber seed exudate. Replacement series experiments with 501R3 and A-11 where initial inoculum levels were above carrying capacity, essentially at carrying capacity, and below carrying capacity, indicated that the importance of carbohydrate in cucumber seed exudate for competitive seed colonization decreases with increased initial population size. Preliminary experiments with 501R3 and M2 provided similar results. Initial disease suppression assays comparing A-11 and 501R3 demonstrated that A-11 provided levels of control of Pythium ultimum damping-off of cucumber that were similar to those of the parental strain, 501R3. These experiments suggest a large degree of nutritional flexibility for E. cloacae during beneficial activities in the spermosphere. Future experiments with M2, M43, and additional, partially characterized mutants of 501R3 will be performed to further examine the role of nutritional flexibility in competitive seed colonization and in disease suppression under various conditions in the spermosphere.