Foreign DNA ‘slips’ through bacterial defenses, promoting antibiotic resistance

A new study from Tel Aviv University has revealed how bacterial defense mechanisms are disabled, allowing efficient transfer of genetic material between bacteria. Researchers believe this discovery could pave the way for the development of tools to address the antibiotic resistance crisis and facilitate more effective genetic engineering methods for medical, industrial and environmental purposes.

This research was led by Drs. Brulia Samuel, a student in the lab of Professor David Burstein at the Shumnis School of Biomedical and Cancer Research at Tel Aviv University’s Wise School of Life Sciences. Other contributors to this research include Dr. Karin Mittelman, Shirley Kreutor, and Maya Benheim from Professor Burstein’s lab. The results of this study were published in the journal Nature.

Researchers explain that genetic diversity is essential for different species to survive and adapt in response to environmental changes. For humans and many other organisms, sexual reproduction is the primary driver of genetic diversity necessary for survival. However, bacteria and other microorganisms do not have such reproductive mechanisms.

Nevertheless, as shown by the alarming rate at which antibiotic resistance spreads among bacterial populations, bacteria have developed alternative strategies to maintain the genetic diversity necessary for their survival, such as direct transfer of DNA between bacteria. It has a mechanism.

DNA transfer between bacteria plays an important role in bacterial survival. However, important aspects of this process remain unknown. Given that bacteria have extensive defense mechanisms designed to destroy foreign genetic material that enters their cells, how is it that the exchange of genetic material is so prevalent?

The new study focuses on one of the key mechanisms for transferring DNA from one bacterium to another, a process called conjugation. During conjugation, one bacterial cell is connected directly to another through a small tube, allowing the transfer of pieces of genetic material known as plasmids.

Professor Burstein said: ‘Plasmids are small circular double-stranded DNA molecules classified as ‘mobile genetic elements’. Like viruses, plasmids move from one cell to another, but unlike viruses, they do not need to kill the host bacteria to complete the transfer. ”

As part of natural exchange, plasmids often provide genetic advantages to recipient bacteria. For example, many antibiotic resistance genes are spread through plasmid transfer between bacteria. However, bacteria also have a number of defense mechanisms aimed at eliminating foreign DNA that enters the cell.

“Conjugation is a well-known process that scientists also use in the laboratory to transfer genes between bacteria. It is also known that bacteria have mechanisms to destroy foreign DNA, including plasmid DNA. Some of these mechanisms have also been used for various research purposes.”However, until now, no one has fully studied how plasmids overcome these defense mechanisms. ” says Professor Burstein.

Samuel explains that the study began by conducting a computer analysis of 33,000 plasmids to identify genes associated with “anti-defense” systems that help plasmids evade bacterial defense mechanisms.

What is even more interesting is the location of these genes. As mentioned above, a plasmid is a double-stranded circular DNA segment. To pass through the thin tubes that connect the bacteria, one of those circular chains is broken at a specific point by a protein that binds to the broken chain and initiates transmission to the recipient cell.

“It turns out that the genes for the anti-defense system that I identified are concentrated near their breakpoints and are organized in such a way that they are the first genes to invade new cells. This strategy This arrangement allows the gene to be activated immediately after transfer, giving the plasmid the advantage it needs to neutralize the recipient bacteria’s defense systems. ”

Professor Burstein tells how when Samuel first showed him the results, he found it hard to believe that such a phenomenon had never been seen before.

“Mr. Bruria did an extensive literature review and found that no one had ever shown a relationship like this before,” he says. Because this discovery was made by analyzing existing databases using computational tools, the next step was to demonstrate in the laboratory that this phenomenon actually occurs during plasmid transfer between bacteria.

“To do this, we used a plasmid that confers antibiotic resistance and introduced it into bacteria equipped with CRISPR, a well-known bacterial defense system that can target and destroy plasmid-containing DNA,” Samuel said. This method has made testing easier.” If the plasmid is successful in overcoming the defense system, i.e. the CRISPR system, the recipient bacteria will become resistant to the antibiotic; if it fails, the bacteria will die. ”

Using this method, Samuel demonstrated that plasmids can successfully overcome the CRISPR system if anti-defense genes are placed close to the DNA entry point. But if these genes are elsewhere on the plasmid, the CRISPR system destroys the plasmid, and the bacteria die when exposed to antibiotics.

Professor Burstein points out that understanding the location of anti-defense systems on plasmids may enable the identification of new anti-defense genes, which are currently undergoing very active research.

“Furthermore, our research can contribute to the design of more efficient plasmids for genetic manipulation of bacteria in industrial processes. Plasmids are already widely used for these purposes, but in the laboratory “The efficiency of plasmid-based gene transfer in these conditions is significantly lower than that of native plasmids,” he says.

“Another potential application could include designing plasmids that are effective in genetically manipulating natural bacterial populations, such as blocking antibiotic resistance genes in hospital bacterial populations; We teach bacteria in soil and water to break down pollutants, fix carbon dioxide, and even manipulate gut bacteria to improve human health.”

Ramot, Tel Aviv University’s technology transfer company, considers this discovery an important biotechnology advance with widespread applications.

Dr Ronen Kreizmann, CEO of Ramot, said: ‘First of all, I would like to congratulate Professor David Burstein and his research team on this fascinating scientific discovery. “This opens up revolutionary possibilities in fields such as the development of drugs against bacteria and synthetic biology.” The ability to control and fine-tune the transfer of genetic material between bacteria could become a powerful tool to address environmental, agricultural, and medical challenges. We are currently working on commercialization to fully realize this technology. Potential. “