Journal of Bacteriology, September 2001, p. 5187-5197, Vol. 183, No. 17
0021-9193/01/$04.00+0 DOI: 10.1128/JB.183.17.5187-5197.2001
Copyright © 2001, American Society for Microbiology. All rights reserved.
Center for Vaccine Development and Department of Microbiology and Immunology, University of Maryland School of Medicine, Baltimore, Maryland 21201,1 and Centro de Investigaciones in Ciencias Microbiologicas, Instituto de Ciencias, Benemerita Universidad Autonoma de Puebla, Puebla, Mexico2
Received 9 February 2001/Accepted 7 June 2001
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 is
responsible for outbreaks of bloody diarrhea and hemolytic-uremic
syndrome in many countries. EHEC virulence mechanisms include the
production of Shiga toxins (Stx) and formation of attaching and
effacing (AE) lesions on intestinal epithelial cells. We recently
reported that genes involved in the formation of the AE lesion were
regulated by quorum sensing through autoinducer-2, which is synthesized by the product of the luxS gene. In this study we
hybridized an E. coli gene array with cDNA synthesized
from RNA that was extracted from EHEC strain 86-24 and its isogenic
luxS mutant. We observed that 404 genes were regulated
by luxS at least fivefold, which comprises approximately
10% of the array genes; 235 of these genes were up-regulated and 169 were down-regulated in the wild-type strain compared to in the
luxS mutant. Down-regulated genes included several
involved in cell division, as well as ribosomal and tRNA genes.
Consistent with this pattern of gene expression, the
luxS mutant grows faster than the wild-type strain
(generation times of 37.5 and 60 min, respectively, in Dulbecco
modified Eagle medium). Up-regulated genes included several
involved in the expression and assembly of flagella, motility, and
chemotaxis. Using operon::lacZ fusions to
class I, II, and III flagellar genes, we were able to confirm this
transcriptional regulation. We also observed fewer flagella by Western
blotting and electron microscopy and decreased motility halos in
semisolid agar in the luxS mutant. The average swimming
speeds for the wild-type strain and the luxS mutant are 12.5 and 6.6 µm/s, respectively. We also observed an increase in the
production of Stx due to quorum sensing. Genes encoding Stx, which are
transcribed along with
-like phage genes, are induced by an SOS
response, and genes involved in the SOS response were also regulated by
quorum sensing. These results indicate that quorum sensing is a global
regulatory mechanism for basic physiological functions of E.
coli as well as for virulence factors.
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