Regulators encoded in the Escherichia coli type III secretion system 2 gene cluster influence expression of genes within the locus for enterocyte effacement in enterohemorrhagic E. coli O157:H7.
Enterohemorrhagic Escherichia coli (EHEC) O157:H7 subverts host cells through a type III secretion system encoded by the locus for enterocyte effacement (LEE). Genome sequencing of this pathotype revealed the existence of a gene cluster encoding components of a second cryptic type III secretion system, E. coli type III secretion system 2 (ETT2). Recently, we showed that the ETT2 gene cluster is present in whole or in part in the majority of E. coli strains but is unable to encode a functional secretion system in most strains, including EHEC O157:H7. However, here we show that mutational inhibition of two regulatory genes (ECs3720 or etrA and ECs3734 or eivF) from the ETT2 cluster in EHEC O157:H7 leads to greatly increased secretion of proteins encoded by the LEE and to increased adhesion to human intestinal cells. Studies in which transcriptional fusions and microarrays were used indicated that EtrA and EivF exert profound negative effects on gene transcription within the LEE. Consistent with these observations, expression of these regulators in an EHEC O26:H- strain led to suppression of protein secretion under LEE-inducing conditions. These findings provide fresh examples of the influence of mobile genetic elements on regulation of the LEE and of cross talk between type III secretion system gene clusters. In addition, they provide a cautionary tale because they show that the effects of regulatory genes can outlive widespread decay of other genes in a functionally coherent gene cluster, a phenomenon that we have named the "Cheshire cat effect." It also seems likely that variations in the ETT2 regulator repertoire might account for strain-to-strain variation in secretion of LEE-encoded proteins.
Zhang
Lihong
L
Bacterial Pathogenesis and Genomics Unit, Division of Immunity and Infection, Medical School, University of Birmingham, Birmingham B15 2TT, United Kingdom.
Chaudhuri
Roy R
RR
Constantinidou
Chrystala
C
Hobman
Jon L
JL
Patel
Mala D
MD
Jones
Antony C
AC
Sarti
Donatella
D
Roe
Andrew J
AJ
Vlisidou
Isabella
I
Shaw
Robert K
RK
Falciani
Francesco
F
Stevens
Mark P
MP
Gally
David L
DL
Knutton
Stuart
S
Frankel
Gad
G
Penn
Charles W
CW
Pallen
Mark J
MJ
D001422:Bacterial Adhesion; D001426:Bacterial Proteins / Q000378:metabolism; D001483:Base Sequence; D002874:Chromosome Mapping; D020895:Enterocytes / Q000382:microbiology*; D019453:Escherichia coli O157 / Q000235:genetics* / Q000472:pathogenicity; D015964:Gene Expression Regulation, Bacterial; D005809:Genes, Regulator; D044404:Genomic Islands / Q000235:genetics*; D006801:Humans; D008969:Molecular Sequence Data; D005810:Multigene Family
D001426:Bacterial Proteins