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Front. Microbiol. | doi: 10.3389/fmicb.2019.01233

Cytosine N4-methylation via M.Ssp6803II is involved in the regulation of transcription, fine-tuning of DNA replication and DNA repair in the cyanobacterium Synechocystis sp. PCC 6803

Katrin Gärtner1,  Stephan Klähn2, 3,  Satoru Watanabe4,  Stefan Mikkat5, Ingeborg Scholz2,  Wolfgang R. Hess2, 6 and  Martin Hagemann7, 8*
  • 1Institut für Pflanzenphysiologie, Universität Rostock, Germany
  • 2Genetics and Experimental Bioinformatics, Faculty of Biology, University of Freiburg, Germany
  • 3Department of Solar Materials, Helmholtz-Centre for Environmental Research, Germany
  • 4Department of Bioscience, Tokyo University of Agriculture, Japan
  • 5Core Facility Proteome Analysis, University Medicine Rostock, Germany
  • 6Freiburger Institut für Höhere Studien (FRIAS), Albert-Ludwigs-Universität Freiburg, Germany
  • 7Institute of Biosciences, University of Rostock, Germany
  • 8Department Leben, Licht & Materie, Interdisziplinäre Fakultät, Universität Rostock, Germany

DNA methylation plays a crucial role for gene regulation among eukaryotes, but its regulatory function is less documented in bacteria. In the cyanobacterium Synechocystis sp. PCC 6803 five DNA methyltransferases have been identified. Among them, M.Ssp6803II is responsible for the specific methylation of the first cytosine in the frequently occurring motif GGCC, leading to N4-methylcytosine (GGm4CC). The mutation of the corresponding gene sll0729 led to lowered chlorophyll/phycocyanin ratio and slower growth. Transcriptomics only showed altered expression of sll0470 and sll1526, two genes encoding hypothetical proteins. Moreover, prolonged cultivation revealed instability of the initially obtained phenotype. Colonies with normal pigmentation and wild-type-like growth regularly appeared on agar plates. These colonies represent suppressor mutants, because the sll0729 gene was still completely inactivated and the GGCC sites remained unmethylated. The suppressor strains showed smaller cell size, lowered DNA content per cell, and decreased tolerance against UV compared to wild type. Promoter assays revealed that the transcription of the sll0470 gene was still stimulated in the suppressor clones. Proteomics identified decreased levels of DNA topoisomerase 4 in suppressor cells. Collectively, these results indicate that GGm4CC methylation is involved in the regulation of gene expression, in the fine-tuning of DNA replication, and DNA repair mechanisms.

Keywords: DNA methyltransferase, DNA topoisomerase, Proteome, Restriction analvsis, Transcripiome analysis, UV tolerance

Received: 15 Feb 2019; Accepted: 17 May 2019.

Edited by:

Weiwen Zhang, Tianjin University, China

Reviewed by:

Feng Ge, Institute of Hydrobiology, Chinese Academy of Sciences, China
Luis Lopez-Maury, University of Seville, Spain  

Copyright: © 2019 Gärtner, Klähn, Watanabe, Mikkat, Scholz, Hess and Hagemann. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY). The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

* Correspondence: Prof. Martin Hagemann, University of Rostock, Institute of Biosciences, Rostock, D-18059, Germany,