Submitted to: International Union of Microbiological Societies Proceedings/Abstracts
Publication Type: Abstract Only
Publication Acceptance Date: July 26, 2005
Publication Date: July 25, 2006
Citation: Roberts, D.P., Hu, X., Mckenna, L.F., Lohrke, S., Kong, H.N., Desouza, J.T., Lydon, J. 2006. Mutation of a cyaa homologue in enterobacter cloacae results in reduced colonization of cucumber seedlings and roots [abstract]. International Union of Microbiological Societies Proceedings/Abstracts.
Background: Enterobacter cloacae is a plant-beneficial bacterium that suppresses damping-off caused by Pythium ultimum on cucumber and other crop plants. We are characterizing a collection of mini-Tn5 Km mutants of E. cloacae strain 501R3 that are affected in colonization of cucumber in an effort to improve our understanding of how this bacterium associates with plant tissues. One mutant, E. cloacae strain M59, was selected for further study after it was found to be reduced in colonization of cucumber and other seeds.
Methods: Populations of strains 501R3 and M59 on cucumber roots were determined by dilution-plating. The nucleotide sequence of both strands of the E. cloacae genome flanking the mini-Tn5 insertion site in M59 was obtained using PCR-mediated Taq DyeDeoxy terminator cycle sequencing and deposited in GenBank under accession number AY765258. Growth of strains on individual compounds in cucumber root exudate and chemotaxis towards these compounds were determined by standard protocols.
Results: Populations of strain M59 were significantly lower (P < 0.0003) than those of strain 501R3 at 21 and 42 days after the addition of these strains as a seed treatment to potting mix or to natural soil. Blast searches with the M59 sequence indicated 85.0 % DNA sequence identity and 91.2 % amino acid sequence identity with the cyaA sequence from E. coli. Analysis of sequence upstream of cyaA indicated the presence of a region of DNA with a high degree of sequence similarity to hemC. Analysis of sequence downstream of cyaA indicated the presence of regions of DNA with a high degree of sequence similarity to cyaY and dapF. These genes have identical organization and direction of transcription in E. cloacae and Escherichia coli. Strain M59 was motile, unlike E. coli cyaA mutants, but was reduced or deficient in chemotaxis towards compounds detected in cucumber root exudate. This strain was also significantly reduced in growth in vitro on most of these compounds.
Conclusions: This data indicates that cyaA is important for colonization of cucumber roots by E. cloacae. This reduction in colonization is presumably due to the role of this gene in growth on, and chemotaxis toward, compounds in cucumber root exudate.