Two novel conditional broad-host-range cell lysis systems have been developed for the study of natural transformation in bacteria and the environmental fate of DNA released by cell death. Plasmid pDKLO2 consists of lysis genes S, R, and Rz from bacteriophage A under the control of the Ptac promoter. The addition of inducer to Escherichia coli, Acinetobacter calcoaceticus, or Pseudomonas stutzeri containing plasmid pDKLO2 resulted in cell lysis coincident with the release of high amounts of nucleic acids into the surrounding medium. The utility of this lysis system for the study of natural transformation with DNA released from lysed cells was assessed with differentially marked but otherwise isogenic donor-recipient pairs of P. stutzeri JM300 and A. cakoacetcus BD4. Transformation frequencies obtained with lysis-released DNA and DNA purified by conventional methods and assessed by the use of antibiotic resistance (P. stutzeri) or amino acid prototrophy (A. cakoaceticus) for markers were comparable. A second cell lysis plasmid, pDKL01, contains the lysis gene E from bacteriophage 4X174 and causes lysis ofE. coli and P. stutzeri bacteria by activating cellular autolysins.Whereas DNA released from pDKL02-containing bacteria persists in the culture broth for days, that from induced pDKLO1-containing bacteria is degraded immediately after release. The lysis system involving pDKL02 is thus useful for the study of both the fate of DNA released naturally into the environment by dead cells and gene transfer by natural transformation in the environment in that biochemically unmanipulated DNA containing defined sequences and coding for selective phenotypes can be released into a selected environment at a specific time point. This will allow kinetic measurements that will answer some of the current ecological questions about the fate and biological potential of environmental DNA to be made.The microbial world is characterized by the collective ability of its members to rapidly colonize and thrive in a vast range of habitats. Some of these environments are characterized by such extreme physical and/or chemical conditions that all other forms of life are excluded. The metabolic opportunism of microbes results, on the one hand, from the exceptional physiological versatility and biochemical diversity of the microbial world as a whole and, on the other, from the ability of individual populations, when under appropriate selection pressure, to rapidly evolve new metabolic potential as a result of the acquisition of new genetic information through mutation and efficient gene transfer mechanisms. Although gene transfer mechanisms such as conjugation, transduction, and transformation have been extensively studied in the laboratory and participating cellular components have been identified and characterized to a considerable extent (for reviews, see, e.g., references 4 and 14), only limited information is available on natural gene transfer in the environment (17). Since genetic flux in microbial communities is a critical component of t...
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