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Applied and Environmental Microbiology, July 2007, p. 4243-4249, Vol. 73, No. 13
0099-2240/07/$08.00+0     doi:10.1128/AEM.00199-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.

Genomic Methylation: a Tool for Typing Helicobacter pylori Isolates{triangledown} ,{dagger}

Filipa F. Vale1 and Jorge M. B. Vítor2*

Faculdade de Engenharia, Universidade Católica Portuguesa, Estrada Octávio Pato, 2635-631 Rio de Mouro, Portugal,1 Centro de Estudos de Ciências Farmacêuticas, Faculdade de Farmácia da Universidade de Lisboa, Av. Prof. Gama Pinto, 1649-019 Lisboa, Portugal2

Received 25 January 2007/ Accepted 1 May 2007

The genome sequences of three Helicobacter pylori strains revealed an abundant number of putative restriction and modification (R-M) systems within a small genome (1.60 to 1.67 Mb). Each R-M system includes an endonuclease that cleaves a specific DNA sequence and a DNA methyltransferase that methylates either adenosine or cytosine within the same DNA sequence. These are believed to be a defense mechanism, protecting bacteria from foreign DNA. They have been classified as selfish genetic elements; in some instances it has been shown that they are not easily lost from their host cell. Possibly because of this phenomenon, the H. pylori genome is very rich in R-M systems, with considerable variation in potential recognition sequences. For this reason the protective aspect of the methyltransferase gene has been proposed as a tool for typing H. pylori isolates. We studied the expression of H. pylori methyltransferases by digesting the genomic DNAs of 50 strains with 31 restriction endonucleases. We conclude that methyltransferase diversity is sufficiently high to enable the use of the genomic methylation status as a typing tool. The stability of methyltransferase expression was assessed by comparing the methylation status of genomic DNAs from strains that were isolated either from the same patient at different times or from different stomach locations (antrum and corpus). We found a group of five methyltransferases common to all tested strains. These five may be characteristic of the genetic pool analyzed, and their biological role may be important in the host/bacterium interaction.

* Corresponding author. Mailing address: Faculdade de Farmácia de Lisboa, Av. Prof. Gama Pinto, 1649-019 Lisboa, Portugal. Phone: (351) 217946400, ext. 280 or 201. Fax: (351) 217946470. E-mail: jvitor{at}ff.ul.pt

{triangledown} Published ahead of print on 4 May 2007.

{dagger} Supplemental material for this article may be found at http://aem.asm.org/.

Applied and Environmental Microbiology, July 2007, p. 4243-4249, Vol. 73, No. 13
0099-2240/07/$08.00+0     doi:10.1128/AEM.00199-07
Copyright © 2007, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Humbert, O., Salama, N. R. (2008). The Helicobacter pylori HpyAXII restriction-modification system limits exogenous DNA uptake by targeting GTAC sites but shows asymmetric conservation of the DNA methyltransferase and restriction endonuclease components. Nucleic Acids Res 36: 6893-6906 [Abstract] [Full Text]  
  • Vale, F.F., Encarnacao, P., Vitor, J. M. B. (2008). A new algorithm for cluster analysis of genomic methylation: the Helicobacter pylori case. Bioinformatics 24: 383-388 [Abstract] [Full Text]  


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