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When a bacterium repairs its damaged DNA to adapt to its environment

DNA is subject to numerous physico-chemical constraints of intra- or extra-cellular origin, which lead to the regular appearance of lesions, including DNA breaks. Faced with this, bacteria have developed repair strategies that can have surprising consequences on the ability of bacteria to adapt to their environment. This is what researchers from the Laboratory of Plant-Microorganism Interactions, LIPM (INRA-CNRS) showed in an article published on December 4, 2018 in the journal Nucleic Acids Research.

Bacterium DNA. © INRA
Updated on 02/25/2019
Published on 02/25/2019

DNA (deoxyribonucleic acid), the biological macromolecule that makes up chromosomes, is a linear sequence of several millions/billions of nucleotides whose precise nature and order determine the genetic information of living organisms. Maintaining the integrity of this molecule is a priority for living beings to ensure the faithful expression and transmission of their genetic heritage. At the scale of a cell, the slightest chromosomal breakage, if not repaired, can have irreversible consequences, including cell death.

How does a bacterium adapt to its environment?

Living beings have developed mechanisms for repairing DNA breaks, one of which, called NHEJ (Non-Homologous End-Joining), consists in bringing the DNA ends together and "gluing" them back together, thus restoring the integrity of the molecule. Unlike other more accurate repair mechanisms, NHEJ sometimes repairs chromosomes at the cost of mistakes"" at the repair junction, which can lead to a change in the local composition of nucleotides and therefore sometimes to a change in the meaning of genetic information (known as mutations).

An outstanding DNA repair machine

By studying the NHEJ repair mechanism in a soil bacterium, Sinorhizobium meliloti, two surprising observations were made:

  • The ability of bacteria to repair breaks by NHEJ increases under stressful environmental conditions, such as when the ambient temperature rises.
  • On the other hand, among the  repair mistakes, the NHEJ system may accidentally integrate a fragment of DNA of foreign origin into the repaired break.

These laboratory observations could be echoed in nature: when bacteria are in adverse environmental conditions, their increased capacity for DNA repair by NHEJ would increase the frequency of mutations in their genome. In addition, stimulating their ability to integrate foreign DNA would make it easier for them to acquire genetic information from other organisms (a process known as "horizontal gene transfer").

These mechanisms, present in many bacterial species, could thus increase their genetic evolution potential, and therefore their ability to adapt to new environmental conditions.

This work was carried out within the Laboratory of Plant-Microorganism Interactions (LIPM), and was supported by INRA through a Young Scientist Contract to Pierre Dupuy, and funding from INRA's Plant Health and Environment Division.

Publication reference

Dupuy, P., Sauviac, L., and Bruand, C. Stress-inducible NHEJ in bacteria: function in DNA repair and acquisition of heterologous DNA. Nucleic Acids Research, 2018 Dec 4. https://doi.org/10.1093/nar/gky1212