A genetic editor altered the DNA of E. coli bacteria right in the gut.
The most famous genetic editor today is CRISPR/Cas: a molecular machine cuts cellular DNA in a specific place so that the cell turns on its DNA repair mechanisms and fixes the defect. Biotechnologists, together with CRISPR/Cas, introduce a template into the cell, according to which it should patch the hole – with the help of a template, any mutation can be introduced into a section of DNA. At the same time, this method has many variations. In some cases, DNA is not cut at all: part of the molecules from CRISPR/Cas are combined, for example, with an enzyme that converts the genetic letters A (nitrogenous base adenine) into the letters G (base guanine). The molecular chimera, due to the parts that it got from CRISPR/Cas, searches for the exact section of DNA that needs to be modified, and the enzyme attached to it does the rest – changes the gene sequence, introduces mutations.
It was this modified editor that the employees of the biotech company Eligo Bioscience used to edit a specific gene in E. coli bacteria. However, the point of the experiment was not so much in the editing itself, but in the fact that it was carried out directly in the intestines of living mice. This is not the first attempt of this kind, but so far in such studies the genetic editor has worked with moderate efficiency. The editing machine must be delivered to the intestines, where it must find the necessary bacterial cells. A bacteriophage virus is usually chosen for delivery: its protein shell is used to deliver DNA with information about the genetic editor directly to the bacterium, and the bacterium itself synthesizes all the parts of the editing machine that will change it.
In cell cultures, bacteriophages with CRISPR/Cas worked well. Problems arose when they tried to destroy microbes in their place of residence, that is, in the intestines, in the same way. The fact is that the virus interacts with bacteria through certain surface receptor molecules, and such receptors may differ in bacteria in laboratory culture and in the natural environment.
This time, the researchers managed to overcome this problem: in their article in Nature They describe modifications of the E. coli-specializing bacteriophage lambda, allowing it to infect cells with different receptors. In addition, the DNA that the virus introduced into the bacterium could not be copied: this required certain regulatory sequences that the bacterium did not have at hand. That is, the genetic editor-modifier recorded in the introduced DNA worked only in the cell where the DNA entered – because it could not have a copy that could go to a daughter cell. The genetic editor was limited to one generation of bacteria.
The gene whose DNA was modified encoded the enzyme β-lactamase. With its help, bacteria neutralize some types of antibiotics. Eight hours after the DNA of the genetic editor in the viral shell was fed to mice, more than 90% of the E. coli in their digestive system turned out to have a modified β-lactamase gene (in some cases, the proportion of bacteria with modification reached 99.7%). In another experiment, it was necessary to change a bacterial gene whose protein plays a certain role in autoimmune diseases – by the end of the third week, this gene was modified in 70% of bacteria.
It is clear that such a biotechnological tool can be used as a medicine or as a medicine enhancer, aimed strictly against certain bacteria. If we want to modify only E. coli that have become resistant to antibiotics, then we modify only them, while, for example, bifidobacteria will remain untouched. (And E. coli that have lost their resistance can then be exterminated with a regular antibiotic that previously did not work against them.) To act on other bacteria, protein shells from other phages can be used as packaging, in addition, these shells can again be modified, adjusting them to other microbes. The researchers themselves, by the way, successfully reconfigured their editor to bacteria Klebsiella pneumoniaecausing pneumonia, only they were modified not in animals, but in cell culture.
Source: www.nkj.ru
