Competence

Competence

	Competence - The recipient bacteria must be competent if they are to accept DNA and undergo transformation .The competence of bacteria is not a permanent feature but occurs only at certain times in the life cycle. The duration and time of occurrence of the competence stages varies with the bacterial species and conditions of growth. Competence is commonly observed towards the end of the logarithmic phase of growth, just before the stationary phase.
In Pneumococcus, competence developed 90-100 minutes after beginning the culture, and lasted for 7-15 minutes (Ephrussi- Taylor and Freed, 1964). In B. subtilis the duration of competence is usually several hours, and only a minority of the cells become competent. Treatment with pronase, a general protein-digesting enzyme, has no effect on the development of competence. Transfer of competence does not take place between cultures.
Competence does not appear to be correlated with cell division, but appears to be the result of establishment of a critical cell concentration. During the competence stage, growth of the cell wall and chromosome replication occur either at a reduced rate or not at all. Protein synthesis, however, continues at the normal rate. Competence develops very rapidly in pneumococcal cultures. The number of competent cells doubles every 3-5 minutes, i. e. at a much faster rate than that of cell growth.
Extracellular factors from competent cultures can induce competence in non competent cells. These competence factors include a heat unstable protein in some cases and a heat-stable molecule in others. The instability of the heat-unstable protein factor may be due to a heat stable inhibitor which cannot diffuse through a membrane. Some competence factors probably work by inducing passage of DNA through the cell envelope.
	Physical contact of cells is not essential for transfer of competence. Competence occurs even when the two cultures are separated by a millipore filter. A dialysis membrane, however, prevents the transfer of competence, indicating that some macromolecule is involve9. The competence factor (CF) has been isolated from competent cells of a Streptococcus strain. It is a small, very basic protein, with MW less than 5,000 daltons. The CF of pneumococcus has a MW of 10,000 daltons.

One theory proposed to explain the development of competence holds that the structure of the cell wall is critical. It permits the uptake of DNA only during the restricted competence phase, and its permeability to macromolecules may change with growth conditions. Another theory holds that competence results from the synthesis of specific receptor sites on the surface of the cell. This view is supported by the fact that synthesis of new protein is necessary for development of competence. Inhibition of protein or RNA synthesis inhibits transformation. It is of course possible that both structural changes and the formation of receptor sites are necessary for development of competence. In pneumococcus, competent cells possess an antigen which is absent from non competent cells.

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