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Journal of Bacteriology, February 2005, p. 1014-1021, Vol. 187, No. 3
0021-9193/05/$08.00+0     doi:10.1128/JB.187.3.1014-1021.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.

Induction of Rapid Detachment in Shewanella oneidensis MR-1 Biofilms

Kai M. Thormann,1 Renée M. Saville,1 Soni Shukla,1 and Alfred M. Spormann1,2,3*

Departments of Civil and Environmental Engineering,1 Biological Sciences,2 Geological and Environmental Sciences, Stanford University, Stanford, California3

Received 30 June 2004/ Accepted 28 October 2004

Active detachment of cells from microbial biofilms is a critical yet poorly understood step in biofilm development. We discovered that detachment of cells from biofilms of Shewanella oneidensis MR-1 can be induced by arresting the medium flow in a hydrodynamic biofilm system. Induction of detachment was rapid, and substantial biofilm dispersal started as soon as 5 min after the stop of flow. We developed a confocal laser scanning microscopy-based assay to quantify detachment. The extent of biomass loss was found to be dependent on the time interval of flow stop and on the thickness of the biofilm. Up to 80% of the biomass of 16-h-old biofilms could be induced to detach. High-resolution microscopy studies revealed that detachment was associated with an overall loosening of the biofilm structure and a release of individual cells or small cell clusters. Swimming motility was not required for detachment. Although the loosening of cells from the biofilm structure was observed evenly throughout thin biofilms, the most pronounced detachment in thicker biofilms occurred in regions exposed to the flow of medium, suggesting a metabolic control of detachability. Deconvolution of the factors associated with the stop of medium flow revealed that a sudden decrease in oxygen tension is the predominant trigger for initiating detachment of individual cells. In contrast, carbon limitation did not trigger any substantial detachment, suggesting a physiological link between oxygen sensing or metabolism and detachment. In-frame deletions were introduced into genes encoding the known and putative global transcriptional regulators ArcA, CRP, and EtrA (FNR), which respond to changes in oxygen tension in S. oneidensis MR-1. Biofilms of null mutants in arcA and crp were severely impacted in the stop-of-flow-induced detachment response, suggesting a role for these genes in regulation of detachment. In contrast, an {Delta}etrA mutant displayed a variable detachment phenotype. From this genetic evidence we conclude that detachment is a biologically controlled process and that a rapid change in oxygen concentration is a critical factor in detachment and, consequently, in dispersal of S. oneidensis cells from biofilms. Similar mechanisms might also operate in other bacteria.

* Corresponding author. Mailing address: James H. Clark Center, E250, Stanford University, Stanford, CA 94305-5429. Phone: (650) 723-3668. Fax: (650) 724-4927. E-mail: spormann{at}stanford.edu.

Journal of Bacteriology, February 2005, p. 1014-1021, Vol. 187, No. 3
0021-9193/05/$08.00+0     doi:10.1128/JB.187.3.1014-1021.2005
Copyright © 2005, American Society for Microbiology. All Rights Reserved.



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