An Investigation of the Molecular Basis of the Spontaneous Occurrence of a Catalase-Negative Phenotype in Helicobacter pylori

Authors: Manos J.; Kolesnikow T.; Hazell S.L.

Source: Helicobacter, Volume 3, Number 1, March 1998 , pp. 28-38(11)

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Abstract:

Background.

The discovery of a highly active catalase in Helicobacter pylori that in some strains may lose its activity has generated strong scientific interest. We have characterized a spontaneous catalase-negative isolate of H. pylori (UNSW-RU1) and sequenced katA in the parent strain and the promoters of both phenotypes as a prelude to understanding the genetic processes leading to the failure to express catalase. Materials and Methods.

Protein extracts from both phenotypes were examined for catalase on 2D-PAGE and analyzed by Western blot-based immuno-analysis. Presence of catalase mRNA was detected by Northern blot. Hi-Fidelity PCR was used to sequence the katA promoter while katA was sequenced using cycle-sequencing. The transcription start site was located by primer extension. Results.

Catalase protein was absent in UNSW-RU1 (KatA^-) by 2D-PAGE and Western blot, as was catalase mRNA by Northern blot, indicating that the cause of the KatA^- phenotype was at the level of transcription. No mutations were found in the promoter region of the KatA^- isolate. The transcription start site was identified 55 bp upstream of the ATG site and putative RNA polymerase binding sites were mapped at “-10” and “-35”. A Fur box was identified 181 bp upstream of the transcription start site. The sequences of an 876 bp ORF and a 366 bp Escherichia coli phnA homologue were identified. Conclusions.

The UNSW-RU1 (KatA^-) phenotype does not express KatA or transcribe katA. The absence of defects in its promoter and a large part of its ORF indicates that loss of activity may be due to a mutation in an accessory gene essential for catalase expression, or to the binding of a repressor preventing katA transcription.

Document Type: Research article

DOI: http://dx.doi.org/10.1046/j.1523-5378.1998.08030.x

Affiliations: 1: School of Microbiology and Immunology, University of New South Wales, Sydney, Australia

Publication date: 1998-03-01

An Investigation of the Molecular Basis of the Spontaneous Occurrence of a Catalase-Negative Phenotype in Helicobacter pylori

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