THE LEUCINE-RESPONSIVE REGULATORY PROTEIN, A GLOBAL REGULATOR OF METABOLISM IN ESCHERICHIA-COLI

Natural genetic transformation is the active uptake of free DNA by bac terial cells and the heritable incorporation of its genetic informatio n. Since the famous discovery of transformation in Streptococcus pneum oniae by Griffith in 1928 and the demonstration of DNA as the transfor ming principle by Avery and coworkers in 1944, cellular processes invo lved in transformation have been studied extensively by in vitro exper imentation with a few transformable species. Only more recently has it been considered that transformation may be a powerful mechanism of ho rizontal gene transfer in natural bacterial populations. In this revie w the current understanding of the biology of transformation is summar ized to provide the platform on which aspects of bacterial transformat ion in water soil, and sediments and the habitat of pathogens are disc ussed. Direct and indirect evidence for gene transfer routes by transf ormation within species and between different species will be presente d, along with data suggesting that plasmids as well as chromosomal DNA are subject to genetic exchange via transformation. Experiments explo ring the prerequisites for transformation in the environment, includin g the production and persistence of free DNA and factors important for the uptake of DNA by cells, will be compiled, as well as possible nat ural barriers to transformation. The efficiency of gene transfer by tr ansformation in bacterial habitats is possibly genetically adjusted to submaximal levels. The fact that natural transformation has been dete cted among bacteria from all trophic and taxonomic groups including ar chaebacteria suggests that transformability evolved early in phylogeny . Probable functions of DNA uptake other than gene acquisition will be discussed. The body of information presently available suggests that transformation has a great impact on bacterial population dynamics as well as on bacterial evolution and speciation.