Competence and Transformation
Berenike Maier
from: Bacillus: Cellular and Molecular Biology (Second edition) (Edited by: Peter Graumann). Caister Academic Press, U.K. (2012)
Abstract
Competence for transformation enables bacteria to take up exogenous DNA. The imported DNA can integrate into the chromosome by homologous recombination or anneal to form a self replicating plasmid. Development of competence in Bacillus subtilis is tightly regulated as a function of cell density during entry into the stationary growth phase. Additionally, competence occurs only in a small subpopulation of B. subtilis cells. Development of competence is switch-like and controlled by the concentration of the master regulator ComK. Quantitative analysis at the single cell level in conjunction with mathematical modeling allowed understanding of development and decline of competence at the systems level. In the current model, a complex regulatory network maintains the concentration of ComK below a threshold concentration for switching into the competent state. In the stationary growth phase, noisy expression of ComK triggers competence development as individual cells reach the threshold concentration due to random fluctuations. Competent cells express specialized proteins (late competence proteins) for binding, importing, and recombining external DNA. Cytosolic and transmembrane proteins accumulate at a single or both cell poles. Application of external DNA triggers movement of various proteins involved in recombination away from the pole, most likely undergoing search for homologous regions on the chromosome. These findings provide good evidence for a concerted action of DNA import and recombination, promoting the idea that a spatially organized and modular multiprotein machine has evolved for efficient transformation. This machine powers efficient and irreversible DNA import and can work against considerable external forces read more ...
