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Open Access Research article

Elevated recombinant clyA gene expression in the uropathogenic Escherichia coli strain 536, a clue to explain pathoadaptive mutations in a subset of extraintestinal E. coli strains

Constance Oben Ayuk Enow1, Jan Oscarsson12, Nikola Zlatkov1, Marie Westermark1, Marylise Duperthuy1, Sun Nyunt Wai1 and Bernt Eric Uhlin1*

Author Affiliations

1 Department of Molecular Biology, the Laboratory for Molecular Infection Medicine Sweden (MIMS), Umeå University, Umeå, S-90187, Sweden

2 Present address: Department of Odontology, Oral Microbiology, Umeå University, Umeå, S-90187, Sweden

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BMC Microbiology 2014, 14:216  doi:10.1186/s12866-014-0216-4

Published: 2 September 2014

Abstract

Background

Analysis of the Escherichia coli collection of reference strains (ECOR) for the presence of the gene locus clyA, which encodes the pore-forming protein ClyA (cytolysin A), revealed that a non-functional clyA locus is common among certain extraintestinal pathogenic E. coli (ExPEC). In fact, all 15 ECOR group B2 strains and several additionally examined extraintestinal pathogenic (uropathogenic (UPEC) and neonatal meningitis (NBM)) E. coli strains contained various ΔclyA alleles.

Results

There are at least four different variants of ΔclyA, suggesting that such deletions in clyA have arisen at more than one occasion. On the basis of this occurrence of the truncated clyA genes, we considered that there may be a patho-adaptive selection for deletions in clyA in extraintestinal pathogenic E. coli. In E. coli K-12 the clyA gene has been viewed as “cryptic” since it is tightly silenced by the nucleoid structuring protein H-NS. We constructed a restored clyA+ locus in derivatives of the UPEC strain 536 for further investigation of this hypothesis and, in particular, how the gene would be expressed. Our results show that the level of clyA+ expression is highly increased in the UPEC derivatives in comparison with the non-pathogenic E. coli K-12. Transcription of the clyA+ gene was induced to even higher levels when the SfaX regulatory protein was overproduced. The derivative with a restored clyA+ locus displayed a somewhat slower growth than the parental UPEC strain 536 when a sub-inhibitory concentration of the antimicrobial peptide Polymyxin B was added to the growth medium.

Conclusions

Taken together, our findings show that the clyA+ locus is expressed at an elevated level in the UPEC strain and we conclude that this is at least in part due to the effect of the SfaX/PapX transcriptional regulators.

Keywords:
ClyA cytolysin; Pathoadaptive mutations; clyA gene expression; Extraintestinal Escherichia coli; SfaX regulatory protein