DNA in the environment: ecological, and therefore societal, implications

Abstract

Microorganisms grow in some environments but not in others, even though most environments are exposed to essentially all microorganisms. Some of the physical, chemical, and biological factors that affect establishment and growth are known. In the 1940’s, it was discovered in the laboratory under controlled conditions that bacteria transfer genes, not only by conjugal transfer (conjugation), but also, unique among all other organisms, via viruses (transduction) and extracellular DNA (transformation). In the late 1960’s, studies began on whether gene transfer contributed to the adaptation of bacteria to changes in their environments, as it had been assumed that mutation was primarily responsible for changes in the genetic composition of bacteria in natural environments. These studies showed that gene transfer occurs in soil — probably the most complex of environments — and that extracellular DNA, either “naked” or in viruses (bacteriophages), became resistant to degradation when bound on surface-active soil particles, such as clay minerals and humic substances, and persisted. Because this extracellular DNA is not expressed in soil, as it is not in a cell and, therefore, is not detected, it was dubbed “cryptic”. If the cryptic genes are “novel” (i.e., contain recombinant DNA and are not naturally present in a bacterium), they could pose a hazard to the environment, as the undetectable genes could persist, even after the introduced engineered bacteria disappeared, and then reappear in another host more adapted to soil. Some novel genes resulted in unanticipated adverse environmental effects, emphasizing that the potential effects of genetically engineered organisms must be evaluated in simulations of the environment to which they are to be released. Another potential hazard is the widespread use of transgenic plants containing genes from bacteria that code for proteins toxic to insects. Although these biotoxins are probably less of an environmental hazard than synthetic chemical pesticides, they can accumulate in soil when bound on surface-active particles and may be toxic to non-target beneficial insects and enhance the enrichment of toxin-resistant target insects. Although there may be many potential benefits from genetic engineering, the release of recombinant DNA to the environment poses potential risks to society, which must be weighed against potential benefits.