coli. For samples that are hard to handle, like cDNA libraries, gDNA, and plasmids larger than 30 kb, it is suggested to use electrocompetent cells that have transformation efficiencies of over 1 x 1010 CFU/µg. This will ensure a high success rate in introducing the DNA and forming a large number of colonies. It’s important to adjust and optimize the electroporation buffer ( Increasing the concentration of the electroporation buffer can result in increased transformation efficiencies ) and the shape, strength, number, and number of pulses these electrical parameters play a key role in transformation efficiency. Chemical transformation Chemical transformation or heat shock can be performed in a simple laboratory setup, typically yielding transformation efficiencies that are adequate for cloning and subcloning applications, approximately 106 CFU/µg. One of the early methods used was a combination of CaCl2 and MgCl2 to treat the cells. However, these methods resulted in transformation efficiencies, with a maximum of 105 - 106 colony forming units (CFU) per microgram of plasmid DNA. Later research found that certain cations, such as Mn2+, Ca2+, Ba2+, Sr2+ and Mg2+ could have a positive effect on transformation efficiencies, with Mn2+ showing the greatest effect. Restriction barriers to an efficient transformation Some bacterial cells have restriction-modification systems that can degrade exogenous plasmids that are foreign to the host cell. This can greatly reduce the efficiency of transformation. This is due to restriction systems in the recipient cells that target and destroy exogenous DNA. These systems recognize exogenous DNA based on differences in methylation patterns. To address this problem, strategies such as altering the methylation of the exogenous DNA using commercial methylases or reducing the restriction activity in the recipient cells have been applied. For example, using methylation-negative mutants or temporarily inactivating the restriction system with heat can reduce the recipient cell's ability to impose restrictions on the exogenous DNA. See also Transformation (genetics) References External links Bacteria Transformation Efficiency Calculator Genetics