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Journal of Bacteriology, November 2004, p. 7610-7617, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7610-7617.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Role of CysE in Production of an Extracellular Signaling Molecule in Providencia stuartii and Escherichia coli: Loss of cysE Enhances Biofilm Formation in Escherichia coli

Gwen Sturgill,1 Christine M. Toutain,2 John Komperda,1 George A. O'Toole,2 and Philip N. Rather1,3*

Departments of Molecular Biology and Microbiology, Case Western Reserve University School of Medicine,1 Research Service, Veterans Affairs Medical Center, Cleveland, Ohio,3 Department of Microbiology and Immunology, Dartmouth Medical School, Hanover, New Hampshire2

Received 10 May 2004/ Accepted 12 August 2004

A mini-Tn5Cm insertion has been identified that significantly reduced the amount of an extracellular activating signal for a lacZ fusion (cma37::lacZ) in Providencia stuartii. The transposon insertion was located immediately upstream of an open reading frame encoding a putative CysE ortholog. The CysE enzyme, serine acetyltransferase, catalyzes the conversion of serine to O-acetyl-L-serine (OAS). This activating signal was also produced by Escherichia coli, and production was abolished in a strain containing a null allele of cysE. Products of the CysE enzyme (OAS, N-acetyl-L-serine [NAS], O-acetyl-L-threonine, and N-acetyl-L-threonine) were individually tested for the ability to activate cma37::lacZ. Only OAS was capable of activating the cma37::lacZ fusion. The ability of OAS to activate the cma37::lacZ fusion was abolished by pretreatment at pH 8.5, which converts OAS to NAS. However, the activity of the native signal in conditioned medium was not decreased by treatment at pH 8.5. In contrast, conditioned medium prepared from cells grown at pH 8.5 exhibited a 4- to 10-fold-higher activity, relative to pH 6.0. Additional genes regulated by the CysE-dependent signal and OAS were identified in P. stuartii and E. coli. The response to the extracellular signal in E. coli was dependent on CysB, a positive activator that requires NAS as a coactivator. In E. coli, a cysE mutant formed biofilms at an accelerated rate compared to the wild type, suggesting a physiological role for this extracellular signal.

* Corresponding author. Present address: Department of Microbiology and Immunology, Emory University School of Medicine, 3001 Rollins Research Center, Atlanta, GA 30322. Phone: (404) 728-5079. Fax: (404) 728-7780. E-mail: prather{at}emory.edu.

Journal of Bacteriology, November 2004, p. 7610-7617, Vol. 186, No. 22
0021-9193/04/$08.00+0     DOI: 10.1128/JB.186.22.7610-7617.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



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