6.27: Transformation

Microbial communities are dynamic environments where cell lysis releases free DNA into the surroundings. Other cells can take up this extracellular DNA through a process known as transformation.

When a cell incorporates this foreign DNA into its genome, resulting in genetic modification, the process is known as transformation. Cells capable of this process are termed competent. Competence can be natural, as observed in certain bacteria and archaea, or artificially induced in the laboratory.

Natural competence provides ecological advantages. For instance, free DNA serves as a nutrient source, supplying essential elements like carbon, nitrogen, and phosphorus. It also facilitates horizontal gene transfer, enabling microorganisms to acquire new traits such as antibiotic resistance or enhanced virulence.

Various proteins regulate the transformation process, which involves multiple steps. Autolysins play a crucial role by creating pores in the cell wall to allow DNA entry. Membrane-associated DNA-binding proteins capture and transport the extracellular DNA across the cell membrane. Once inside the cell, nucleases degrade one strand of the DNA, leaving a single strand available for integration. Competence-specific proteins protect this single-stranded DNA from degradation, maintaining its integrity until integration occurs.

A recombinase enzyme called RecA mediates strand exchange through homologous recombination, facilitating the integration of the foreign DNA into the host genome. The recombinant cell passes on the integrated DNA to its progeny.

In laboratory settings, transformation is artificially induced using methods like electroporation. This technique involves applying high-voltage electrical pulses to transiently increase cell membrane permeability, enabling the uptake of foreign DNA. Electroporation is commonly used in various cells, including bacteria, yeast, and plant cells, for genetic engineering and research.