Fate of genetically-engineered bacteria in activated sludge microcosms.

The conclusions that can be derived from this study regarding the fate of the GEMs and their ability to degrade added pollutants are as follows: 1. Both GEMs were able to survive in the microcoms. Because Pseudomonas sp. B13 has been cultured for a long time in the laboratory, it was not expected to survive well in the microcosm. Surprisingly, it and the derivative GEMs persisted at a high population level of approximately 10(5) bacteria/ml. Pure culture studies had demonstrated an ability of FR1(pFRC20P) to readily degrade simultaneous mixtures of 3CB and 4MB. In the microcosms, however, the GEM did not perform as well as expected, particularly when confronted with a shock load of a 3CB and 4MB mixture. Thus, the microcosm studies may be of potential help for making predictions concerning environmental applications of GEMs. 2. Pseudomonas sp. B13 derivative strains FR1 and FR1(pFRC20P) were able to degrade low concentrations of substituted benzoates within the complex ecosystem of the activated sludge microcosm. A good deal of information concerning the degradation pathway for aromatics by Pseudomonas sp. B13 was already known. This allowed for the construction of the stable, regulated pathways for the degradation of substituted aromatic compounds in both GEMs and indicates that the construction of similar GEMs for the degradation of environmental pollutants is a promising experimental strategy. 3. There was not any demonstrable, adverse effect of GEM addition to the microbial population level in the microcosm. The GEMs were even able to function in a protective manner for the indigenous populations by buffering them against the adverse effects of addition of substituted benzoates. In contrast, for microcosms lacking GEM addition, a wash-out of the bacterial population in the microcosm occurred (data not shown). 4. Lateral transfer of new genetic information (xylXYZLS) from the GEM chromosome to indigenous microorganisms was not detected, whereas transfer of the hybrid, mobilizable pFRC20P carrying the gene for lactone isomerase did apparently occur. In this particular case, transfer may have been beneficial for the community as a whole if it increased the ecosystem's ability to cope with the presence of toxic pollutants. As more GEMs are constructed for specific biotechnological applications the diversity and complexity of microcosms used to study their fate and function will increase. The ability of such studies to predict a priori the fate of these microorganisms will help to develop strategies both to decrease the risks associated with introducing GEMs into the environment and to increase and regulate the capacity of GEMs to degrade toxic pollutants.(ABSTRACT TRUNCATED AT 400 WORDS)