Characterization of Siderophore Production by the Biological Control Agent Enterobacter cloacae. Jose M Costa. U.S Department of Agricultural, Agricultural Research Service, Horticultural Crops Research Laboratory, 3420 N.W. Orchard Avenue. Joyce E. Loper. Department of Botany and Plant Pathology, Oregon State University, Corvalis 97330. MPMI 7: 440-448. Accepted 25 March 1994. This article is in the public domain and not copyrightable. It may be freely reprinted with customary crediting of the source. The American Phytopathological Society, 1994.

Enterobacter cloacae EcCT-501, which suppresses Pythlium damping-off of cucumber and other plant hosts, produces the hydroxamate siderohore aerobactin and a catechol siderophore tentatively identified as enterobactin. Cloned fragments of genomic DNA of E. cloacae EeCT-501 complemented the enterobactic (ent) biosynthesis mutations entA, entB, entC, entE, and entF of Escherichia coli. By complementation of ent mutations of E. coli, we localized the ent(CEB) A region to a 4.5-kb HindIII-Xho I fragment of the E. cloacae genome and the entA gene to a 1.8-kb EcoRI-Xho I fragment within the ent(CEB)A region. We deleted a 0.8-kbEcoRV fragment internal to the entA genomic region of E. cloacae EcCT-501 to construct mutants deficient in enterobactin production (Ent-). Introduction of this deletion into a derivative of EcCT-501 that was deficient in aerobactin production (luc-) resulted in a mutant deficient in the production of both enterobactin and aerobactin (Ent- luc-). Strain EcCT-501 and the Ent- luc+ and Ent+ luc- deratives grew on an ironlimited medium. The Ent- luc- mutant, however, failed to grow on the iron-limited medium, indicating that both aerobactin and enterobactic function in iron acquisition by E. cloacae. Aerobactin and enterobactin production by E. cloacae did not contribute to its activity in biological control of Pythium damping-off of cotton or cucumber.