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Behind the transformation process: How do bacteria cleverly absorb DNA to improve their survival ability?
In the study of microbiology and cell biology, "ability" refers to the ability of cells to change their genome by absorbing foreign DNA from the environment. This process is called "transformation." The difference between the natural ability of bacteria and the artificially induced ability is that natural ability is generated under natural genetic settings in the natural environment and laboratory, while artificial ability is achieved through laboratory processing that allows cells to instantly penetrate DNA. This ability enables cells to quickly adapt to environmental changes and repair DNA, significantly enhancing their ability to survive.
The study of natural abilities began in 1928, when scientist Frederick Griffiths discovered that dead pathogenic bacteria could change the genotype of harmless bacteria.
With Griffith's discovery in 1928, Oswald Avery and others further confirmed in 1944 that this "transformation factor" was pure DNA, thus revealing that DNA is the carrier of cellular genetic information.
Mechanism of DNA uptake
In the laboratory, scientists usually provide exogenous DNA, which is mostly genetically engineered fragments or plasmids. Cells use specific mechanisms to transport this DNA into the interior of the cell. After DNA enters cells, it may be degraded into nucleotides and used for DNA replication or other metabolic functions. Alternatively, it may be reassembled into the cell's genome by DNA repair enzymes, and if the recombination changes the cell's genotype, the cell is considered transformed.
In many naturally competent bacteria, specific external filamentous structures bind to double-stranded DNA and deliver it through multi-component protein complexes.
Regulation of abilities
During laboratory cultivation, natural abilities are often tightly regulated and often triggered by nutritional deficiencies or adverse environmental conditions. However, the specific induction signals and regulatory mechanisms vary widely in different species. Scientists have discovered that some transcription factors regulate the formation of abilities, such as sxy (also known as tfoX). In bacteria that can form spores, the conditions that induce spores often coincide with the conditions that induce competence. Therefore, cultures containing sporulating cells will often also have competent cells.
Evolutionary functions and consequences of abilities
Today's major proposals for the evolutionary function of natural abilities generally fall into three categories: selective advantages affecting genetic diversity; DNA uptake as a source of nucleotides; and selective advantages for repairing damaged DNA through homologous recombination.
Some studies have suggested that bacterial transformation may play a role similar to the sexual behaviors of higher organisms in increasing genetic diversity, but this view also has some theoretical difficulties.
Another hypothesis is that DNA serves as a source of food, because cells that ingest DNA receive the nucleotides that this DNA is made of, which are essential for DNA and RNA synthesis.
Hypothesis of DNA damage repair
In bacteria, DNA damage problems are most apparent during periods of stress, particularly oxidative stress in conditions of crowding or starvation. Therefore, some bacteria induce competence under these stresses, supporting the hypothesis that transformation aids DNA repair. Experiments have shown that cells that have undergone DNA damage treatment and undergo transformation have a higher survival rate than damaged cells that have not been transformed.
Horizontal gene transfer
Although this ability may bring long-term benefits to the bacteria, in some cases it may also result in resistance or other advantages through different combinations of genes. The complex nature of the genome highlights the ability of bacteria to enable horizontal gene transfer to help increase genetic diversity and thereby support their evolution.
Facing a rapidly changing environment, how do bacteria cleverly use this ability to stabilize themselves and adapt to the outside world?
