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Journal of Bacteriology, November 2007, p. 8005-8014, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00566-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Motility and Chemotaxis in Agrobacterium tumefaciens Surface Attachment and Biofilm Formation ^,

Peter M. Merritt, Thomas Danhorn, and Clay Fuqua^*

Department of Biology, Indiana University, Bloomington, Indiana 47405

Received 12 April 2007/ Accepted 24 August 2007

Bacterial motility mechanisms, including swimming, swarming, and twitching, are known to have important roles in biofilm formation, including colonization and the subsequent expansion into mature structured surface communities. Directed motility requires chemotaxis functions that are conserved among many bacterial species. The biofilm-forming plant pathogen Agrobacterium tumefaciens drives swimming motility by utilizing a small group of flagella localized to a single pole or the subpolar region of the cell. There is no evidence for twitching or swarming motility in A. tumefaciens. Site-specific deletion mutations that resulted in either aflagellate, flagellated but nonmotile, or flagellated but nonchemotactic A. tumefaciens derivatives were examined for biofilm formation under static and flowing conditions. Nonmotile mutants were significantly deficient in biofilm formation under static conditions. Under flowing conditions, however, the aflagellate mutant rapidly formed aberrantly dense, tall biofilms. In contrast, a nonmotile mutant with unpowered flagella was clearly debilitated for biofilm formation relative to the wild type. A nontumbling chemotaxis mutant was only weakly affected with regard to biofilm formation under nonflowing conditions but was notably compromised in flow, generating less adherent biomass than the wild type, with a more dispersed cellular arrangement. Extragenic suppressor mutants of the chemotaxis-impaired, straight-swimming phenotype were readily isolated from motility agar plates. These mutants regained tumbling at a frequency similar to that of the wild type. Despite this phenotype, biofilm formation by the suppressor mutants in static cultures was significantly deficient. Under flowing conditions, a representative suppressor mutant manifested a phenotype similar to yet distinct from that of its nonchemotactic parent.

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* Corresponding author. Mailing address: Department of Biology, Indiana University, 1001 E. 3rd St., Jordan Hall 142, Bloomington, IN 47405-1847. Phone: (812) 856-6005. Fax: (812) 855-6705. E-mail: cfuqua{at}indiana.edu

Published ahead of print on 31 August 2007.

Supplemental material for this article may be found at http://jb.asm.org/.

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Journal of Bacteriology, November 2007, p. 8005-8014, Vol. 189, No. 22
0021-9193/07/$08.00+0     doi:10.1128/JB.00566-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

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