EnterohemorrhagicEscherichia coliBiofilms Are Inhibited by 7-Hydroxyindole and Stimulated by Isatin

Abstract

Since indole is present at up to 500 M in the stationary phase and is an interspecies biofilm signal (J. Lee, A. Jayaraman, and T. K. Wood, BMC Microbiol. 7:42, 2007), we investigated hydroxyindoles as biofilm signals and found them also to be nontoxic interspecies biofilm signals for enterohemorrhagic 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 in biofilm cells were repressed compared to those in 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 fourfold for EHEC, while it had no effect for K-12. When continuous-flow chambers were used, confocal microscopy revealed that 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 that 7-hydroxyindole inhibits E. coli biofilm through cysteine metabolism. 7-Hydroxyindole (500 M) also stimulates P. aeruginosa PAO1 biofilm formation twofold; therefore, hydroxyindoles are interspecies bacterial signals, and 7-hydroxyindole is a potent EHEC biofilm inhibitor.Procaryotes and eucaryotes signal not only themselves but also one another; hence, there is competition and interference of cell signals. For example, interference of acylhomoserine lactones (AHLs) is manifested by AHL lactonases and acylases, which are present in both gram-positive and gram-negative bacteria (79). Similarly, autoinducer-2 (AI-2), a furanosyl borate diester or derivative (39), may be manipulated by Escherichia coli and Vibrio harveyi to interfere with the ability of each species to assess changes in cell population (75). This competition extends beyond procaryotes, as eucaryotes manipulate the quorum-sensing signals of bacteria, too. For example, algae block bacterial biofilm formation via furanones by controlling both AHL signaling (25) and AI-2 signaling (52), and mammals (including humans) block AHL signaling via lactonase in sera (76). Analogously, bacteria take advantage of eucaryotic signals since enterohemorrhagic E. coli O157:H7 (EHEC) bacteria utilize the human hormones epinephrine and norepinephrine to activate virulence genes (33), and bacteria inter...

YqhD: a broad-substrate range aldehyde reductase with various applications in production of biorenewable fuels and chemicals

“…coli had increased transcript abundance of yqhD in biofilm-associated cells treated with isatin relative to planktonic cells also treated with isatin (Lee et al 2007). Isatin is an oxidized indole with two ketone groups and was being investigated due its role as a potential signaling molecule.…”

Escherichia coli transcription factor YncC (McbR) regulates colanic acid and biofilm formation by repressing expression of periplasmic protein YbiM (McbA)

“…A series of genes including bssR/bssS, bhsA and ariR have been identified as regulating biofilm formation through indole (Domka et al, 2006;Lee et al, 2007c;Zhang et al, 2007), and hydroxy indoles have been shown to be signals for pathogenic E. coli Lee et al, 2007a).…”

A Proton Wire and Water Channel Revealed in the Crystal Structure of Isatin Hydrolase

“…In prokaryotes, isatin has been identified as a signaling molecule in biofilm formation and during chemotactic response. Biofilm formation by enterohemorrhagic Escherichia coli increased 4-fold when exposed to isatin (11). Cellular migration toward higher isatin concentration was observed when E. coli were subjected to isatin concentration gradients (12).…”