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Appl. Environ. Microbiol. doi:10.1128/AEM.00360-07
Copyright (c) 2007, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Enterohemorrhagic Escherichia coli Biofilms Are Inhibited by 7-Hydroxyindole and Stimulated by Isatin

Artie McFerrin Department of Chemical Engineering, the Department of Biology, and the Zachry Department of Civil Engineering, 220 Jack E. Brown Building, Texas A & M University, College Station, TX 77843-3122; Fischell Department of Bioengineering, University of Maryland, College Park, Maryland 20742

^* To whom correspondence should be addressed. Email: Thomas.Wood{at}chemail.tamu.edu.

	Abstract

Since indole is present at up to 500 µM in the stationary phase and is an interspecies biofilm signal (J. Lee, A. Jayaraman, and T. K. Wood, BMC Microbiol., in revision, 2007), we investigated hydroxyindoles as biofilm signals and found them also to be non-toxic interspecies biofilm signals for Escherichia coli O157:H7 (EHEC), E. coli K-12, and Pseudomonas aeruginosa. The genetic basis of EHEC biofilm formation was also explored and notably virulence genes were repressed in biofilm cells compared to planktonic cells. In Luria-Bertani medium (LB) on polystyrene with quiescent conditions, 7-hydroxyindole decreased EHEC biofilm formation 27-fold and decreased K-12 biofilm formation 8-fold without affecting the growth of planktonic cells. 5-Hydroxyindole also decreased biofilm formation 11-fold for EHEC and 6-fold for K-12. In contrast, isatin (indole-2,3-dione) increased biofilm formation 4-fold for EHEC while it had no effect K-12. Using continuous flow chambers, confocal microscopy revealed EHEC biofilm formation was reduced 6-fold by indole and 10-fold by 7-hydroxyindole in LB. Whole transcriptome analysis revealed that isatin represses indole synthesis by repressing tnaABC 7- to 37-fold in EHEC, and extracellular indole levels were found to be 20-fold lower. Furthermore, isatin repressed the AI-2 transporters lsrABCDFGKR, while significantly inducing the flagellar genes flgABCDEFGHIJK and fliAEFGILMNOPQ (which led to a 50% increase in motility). 7-Hydroxyindole induces the biofilm inhibitor/stress regulator ycfR and represses cysADIJPU/fliC (which led to a 50% reduction in motility) and purBCDEFHKLMNRT. Isogenic mutants showed 7-hydroxyindole inhibits E. coli biofilm through cysteine metabolism. 7-Hydroxyindole (500 µM) also stimulates P. aeruginosa PAO1 biofilm formation 2-fold; therefore, hydroxyindoles are interspecies bacterial signals, and 7-hydroxyindole is a potent EHEC biofilm inhibitor.

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