Cell Competency
By Gunisha Aggarwal | 20 September 2024
Competency refers to the cell's potential of taking DNA fragments from the environment to the inside of the cell.
This process is found naturally in many bacterial species. The natural competence helps to uptake DNA from surroundings and incorporate it in the cell's own genome, which will allow it to get transformed. Sometimes a fragment can be uptaken and only used for nutritional purposes without it getting attached to the genome. Frederick Griffith discovered the process in Streptococcus pneumoniae. It differs from artificial competence in being genetically encoded. Also, the regulation of natural competence is dependent on multiple genes.
There is another process referred to as artificial competence where the cells are artificially made competent by certain ways. This is done to aid in cloning, that is, so as to incorporate genetic segments of interest into the genetic material of the host cell.
For transformation to take place we require the DNA to pass the outer and inner cell membrane. There are various physical and chemical ways of doing it. DNA is hydrophilic and hence cannot pass cell membrane. Thus, top achieve competence, small pores are artificially induced in the cell surface which allow its internalisation.
There are various ways of making a cell competent.
Chemical Methods
Bacteria like E.coli when soaked in salt solutions achieve competence. Mandel and Higa in 1970 discovered that when treated with an ice cold solution of calcium chloride followed by brief heating at 37/42 °C, bacteria can be transfected with bacteriophage λ DNA. Similar methods were used for competency later on for plasmid DNA transformation in cells like E. coli.
Ice cold salt solutions like calcium and magnesium chloride accompanied by heat shock (immediate increase of temperature, which creates thermal instability and increases the permeability) are most commonly used to create small pores and this membrane permeabilisation helps in DNA uptake. The salt with divalent positively charged ions neutralise the negative charge on DNA, which reduces the repulsive forces to an extent which brings the DNA near the cell surface. Subsequenly, by heat shock, pores are created that allows the DNA to enter in the cell.
Physical Methods
(a) Electroporation
This method uses a high voltage electrical pulse to create transient pores in the membrane. When cells are supplied with an electric shock, the membrane orientation arranges itself in such a way that a gap is created. These gaps or small transient pores allow for DNA uptake. Here, the cell's own material can be also lost. Also. the pores are transient, which means they form for a very small duration of time.
(b) Freeze - thaw method
This technique is least uses rapid freezing and thawing. Cells are rapidly frozen in liquid nitrogen or kept at -80°C and then rapidly thawed at 37°C. This physically disrupts the cell membrane.
Competent cells are very important in research in the field of molecular biology and other related fields. It is a very crucial technique for manipulating the genetic material for achieving targeted results and scientific advancements.
References
- Sambrook J, Russel D. Molecular Cloning: A Laboratory Manual. 3rd edition. Vol. 1. New York, NY, USA: Cold Spring Harbor Laboratory Press; 2001.
- Blokesch, M. (2016). Natural competence for transformation. Current Biology, 26(21), R1126-R1130.