转化

Transformation is the process by which a cell takes up free DNA released from lysed cells and stably integrates it into its genome. Cells capable of this process are called competent. This mechanism enables bacteria and archaea to acquire new genetic material from their environment, facilitating horizontal gene transfer and providing access to nutrients like carbon, nitrogen, and phosphorus.

Competence involves multiple proteins that regulate DNA uptake. Autolysins create pores in the cell wall, increasing permeability. Membrane-associated DNA-binding proteins capture and transport extracellular DNA across the membrane. Nucleases degrade one DNA strand while competence-specific proteins protect the other strand until homologous recombination integrates it into the host genome.

RecA is a recombinase enzyme that mediates strand exchange through homologous recombination. It facilitates the integration of foreign DNA into the host genome by catalyzing the exchange between the incoming single-stranded DNA and the homologous chromosomal DNA. This ensures stable incorporation of the foreign genetic material into the cell's genome.

Electroporation is a common laboratory technique for artificial transformation. High-voltage electrical pulses create charge separation across the cell membrane, forming transient pores that increase permeability. This allows foreign DNA to enter the cell. Electroporation is widely used in bacteria, yeast, and plant cells for genetic engineering and research applications.

Natural competence offers bacteria and archaea significant ecological benefits. Free DNA serves as a nutrient source, supplying essential elements like carbon, nitrogen, and phosphorus. Additionally, competence facilitates horizontal gene transfer, enabling microorganisms to acquire advantageous traits such as antibiotic resistance or enhanced virulence, increasing their survival and adaptability in changing environments.

Once foreign DNA is integrated into the host genome through homologous recombination, the recombinant cell passes the integrated DNA to its progeny during cell division. This results in a genetically altered lineage where all descendant cells inherit the new genetic material, making the transformation a heritable genetic change.

During transformation, nucleases degrade one strand of the incoming double-stranded DNA, leaving a single strand. Competence-specific proteins then protect this single-stranded DNA from further degradation, maintaining its integrity until homologous recombination can integrate it into the host chromosome. This protection is essential for successful transformation.