Mutation in <Emphasis Type="Italic">cyaA</Emphasis> in <Emphasis Type="Italic">Enterobacter cloacae</Emphasis> decreases cucumber root colonization |
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| Authors: | Daniel P Roberts Laurie F McKenna Xiaojia Hu Scott M Lohrke Hye Suk Kong Jorge T de Souza C Jacyn Baker John Lydon |
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| Institution: | (1) Sustainable Agricultural Systems Laboratory, USDA-Agricultural Research Service, Bldg. 001, Rm. 140, 10300 Baltimore Avenue, Beltsville, MD 20705-2350, USA;(2) Oil Crops Research Institute, Chinese Academy of Agricultural Sciences, Baojian, Wuchang, Wuhan, 430062, People’s Republic of China;(3) Wye Research and Education Center, University of Maryland, Queenstown, MD 21658, USA;(4) Molecular Plant Pathology Laboratory, USDA – Agricultural Research Service, Bldg. 004, 10300 Baltimore Avenue, Beltsville, MD 20705, USA;(5) Present address: Naval Health Research Center, Environmental Health Effects Laboratory, Geo-Centers, Inc., Wright-Patterson Air Force Base, OH 45433, USA;(6) Present address: Laboratory of Methods Development, CBER, FDA, Rockville, MD 20852, USA;(7) Present address: CEPLAC/CEPEC/SEFIT, Caixa Postal 7, Km 22, Rodovia Ilheus-Itabuna, BA, Brazil |
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| Abstract: | Strains of Enterobacter cloacae show promise as biological control agents for Pythium ultimum-induced damping-off on cucumber and other crops. Enterobacter cloacae M59 is a mini-Tn5 Km transposon mutant of strain 501R3. Populations of M59 were significantly lower on cucumber roots and decreased much more
rapidly than those of strain 501R3 with increasing distance from the soil line. Strain M59 was decreased or deficient in growth
and chemotaxis on most individual compounds detected in cucumber root exudate and on a synthetic cucumber root exudate medium.
Strain M59 was also slightly less acid resistant than strain 501R3. Molecular characterization of strain M59 demonstrated
that mini-Tn5 Km was inserted in cyaA, which encodes adenylate cyclase. Adenylate cyclase catalyzes the formation of cAMP and cAMP levels in cell lysates from
strain M59 were approximately 2% those of strain 501R3. Addition of exogenous, nonphysiological concentrations of cAMP to
strain M59 restored growth (1 mM) and chemotaxis (5 mM) on synthetic cucumber root exudate and increased cucumber seedling
colonization (5 mM) by this strain without serving as a source of reduced carbon, nitrogen, or phosphorous. These results
demonstrate a role for cyaA in colonization of cucumber roots by Enterobacter cloacae. |
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| Keywords: | Biological control Colonization Cyclic AMP cyaA Rhizosphere |
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