DNA Crystals Help Bacteria Respond to Stress


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DNA becomes remarkably organized in bacteria that are subjected to various conditions of stress, Weizmann Institute scientists reported in the July 1 issue of Nature. The tightly packed structure promotes the ability of the cells to withstand extreme environmental assaults such as oxidating agents and starvation.

The finding may one day contribute to the development of more general methods against bacterial diseases. In addition, if a link is found between the mechanisms allowing bacteria to survive under stress, and those that render bacteria resistant against various chemical agents, chemotherapy could be efficiently used against pathological bacteria which have become resistant towards other methods.

The Weizmann team, headed by Prof. Avi Minsky of the Organic Chemistry Department, discovered that bacterial DNA forms a crystalline organization when bacteria are exposed to harsh conditions. They further revealed that this highly ordered structure is mediated by a protein called Dps which strongly binds DNA to form a very stable structure. The Dps protein, initially characterized by the group of Prof. Roberto Kolter at Harvard Medical School with which Prof. Minsky collaborates, is present in stressed cells at high levels. Within the ordered and tightly packed DNA-Dps structure, the DNA is very effectively protected against various assaults.

"In natural environments, bacterial life alternates between short periods of feast and long periods of famine and stress." says Prof. Minsky. "In order to survive, bacteria have evolved sophisticated mechanisms that allow them to protect themselves during starvation and stress, as well as to very rapidly resume growth when nutrients are again available. The ordered DNA structure may represent the ultimate mode of protection."

The scientists used X-ray and electron microscopy techniques. They are currently using these techniques to uncover the molecular structure of the complex between the Dps protein and the DNA, in order to better understand the mode of DNA protection. "We are currently investigating the actual signal that triggers the formation of the crystalline structure once subjected to starvation or stress and the signal that effects its fast disappearance once stress is eliminated," says Minsky.

Minsky: "Order is generally considered to be incompatible with life. However, in living systems exposed to severe environmental assaults, intracellular crystalline assemblies may confer an efficient means for wide range protection. Indeed, ribosomes in brain cells of people suffering from dementia were found to form crystalline organizations. Moreover, DNA in sperm cells is highly ordered. We have now found this to be true in bacterial DNA as well and are trying to understand how general and significant the correlation between order and survival is."

Accordingly, the Weizmann team has recently begun to study the correlation between the organization of DNA and fertility in human sperm cells.
The Weizmann Institute of Science is a major scientific research graduate study located in Rehovot, Israel. Its 2,500 scientists, students and support staff are engaged in more than 1,000 research projects across the spectrum of contemporary science.