Our friends are bacteria
A brief history of cooperation between bacteria and humans
How bacteria became a tool for creating organisms with altered properties
Bacteria were among the first organisms whose genomes were altered in the laboratory. Today, these creatures help biotechnologists achieve interesting results. We tell a brief history of the use of bacteria in genetic engineering.
Discovery of bacterial transformation
In 1928, the English geneticist and physician Frederick Griffith discovered the phenomenon of bacterial transformation. At that time, he was developing a vaccine for pneumonia. Working with two strains of bacteria Streptococcus pneumoniae, one of which caused pneumonia in mice, and the other did not, he noticed that if you mix dead virulent bacteria with live non–virulent ones and inject this mixture into mice, they die. It turned out that initially non-virulent bacteria acquired the ability to cause disease and began to transmit it by inheritance. Griffith suggested that there was some kind of "transformative factor" that turned bacteria into pathogenic. In 1944, scientists Avery, McLeod and McCarthy showed that the "transforming factor" in this process is the DNA molecule. Thus, bacteria can actively assimilate other people's DNA fragments and change their own properties.
Development of genetic engineering tools
Plasmids, discovered in 1952, have become important tools for transferring information between cells and replicating DNA sequences. These small DNA molecules, separate from genomic chromosomes and capable of replicating autonomously, are found in bacteria and are a natural means of horizontal transfer – a process in which an organism transfers genetic material to a non-descendant organism. In 1967, enzymes were discovered that connect broken DNA, the so–called ligases. And in 1970, Hamilton Smiths' laboratory discovered restriction enzymes that made it possible to cut DNA in certain places and isolate individual genes from the genome of an organism. The combined use of these two enzymes made it possible to cut and insert DNA sequences into the genome to create new, recombinant DNA. In 1977, Frederick Sanger developed a method of DNA sequencing, which significantly expanded the range of available genetic information. The polymerase chain reaction, discovered in 1983 by American biochemist Cary Mullis, made it possible to copy small sections of DNA, as well as identify and isolate genetic material. For this discovery, the scientist received the Nobel Prize ten years later.
E.coli and insulin production
In 1974, Herbert Boyer and Stanley Norman Cohen obtained the first bacterium carrying a eukaryotic gene, the frog ribosomal RNA gene. And in 1978-1979, Genentech produced the first recombinant proteins, somatotropin and insulin, with the help of Escherichia coli. The human insulin gene was introduced into the genome of the bacterium, and it began to synthesize an insulin analog on its own. Today, modified E. coli are used in the development of vaccines, enzyme synthesis and for many other tasks.
Agrobacterium tumefaciens and plant genetic engineering
Today, one of the most popular methods of introducing a vector – a DNA or RNA molecule that serves to transfer genetic material into the cell – is the use of soil bacteria Agrobacterium tumefaciens. It is often used in plant genetic engineering. At first, the alien genetic material was physically introduced into the plant cell. However, in the same years, the "natural" mechanism of gene transfer was discovered. Sometimes there are balls in the stems of plants that look like a tumor – this is a symbiosis of a plant and a soil bacterium Agrobacterium tumefaciens. It turned out that the bacterium forces the plant to produce a product necessary for its vital activity by transferring part of the gene into a plant cell. Later, scientists figured out how to use this property in genetic engineering. Special plasmid-based vectors were developed that made it possible to introduce new information into the genome and obtain plants with the desired beneficial traits. However, this bacterium is not able to modify cereals, and a gene gun is used to change their DNA.
With the help of Agrobacterium tumefaciens, biotechnologists obtain both food crops and ornamental plants. For a long time, breeders unsuccessfully tried to create blue roses that do not exist in nature. Of course, you can put a white rose in a dye for this. However, Chinese researchers have found a way to turn a rose blue using genetic engineering. The plasmids of Agrobacteria contained two pigment-producing genes idgS and sfp taken from other bacterial species. Bacteria were introduced into the petal of a white rose, and as a result of gene expression, enzymes were obtained that convert the L-glutamine contained in the petals of the flower into the blue pigment indigoidin. Starting from the site of the introduction of bacteria, the petal began to turn blue. Although the color turned out to be uneven and short-lived, scientists said that this is the world's first real blue rose and that the next step will be to create a plant that produces these enzymes independently, without artificial introduction of bacteria.
CRISPR/Cas9
The CRISPR/Cas9 system, based on the mechanism of protection of bacteria from viruses, is now called the most accurate method of gene editing. This system is based on special sections of bacterial DNA, short palindromic cluster repeats, or CRISPR. Between them are different fragments of DNA spacers. Many spacers correspond to sections of the genomes of phage viruses that parasitize bacteria. When a virus enters a bacterial cell, it is detected by CAS proteins that bind to CRISPR. If the system identifies a virus fragment, the proteins cut the viral DNA, destroying it. In the 1980s, Japanese scientists discovered the CRISPR system, in the early 2000s it turned out that spacer sequences were similar to virus sequences, and CAS genes were discovered around the same time. In 2013, scientists showed that these systems can work not only in bacterial cells, but also in more complex organisms, which means the ability to correct incorrect gene sequences and treat hereditary diseases.
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