Persistence of genetically engineeredErwinia carotovora in perturbed and unperturbed aquatic microcosms and effect on recovery of indigenous bacteria.

Genetically engineeredErwinia carotovora persisted significantly longer in thermally perturbed microcosms (35 days) than in nonstressed microcosms (5 days). Decreased pressure of competitors and predators and increased nutrient availability were examined as the most probable reasons for greater vulnerability of perturbed microcosms to colonization by genetically engineered microorganisms (GEMs). Indigenous bacteria that competed with GEMs for the same nutrient sources (protein, cellulose, pectate) were present immediately after perturbation in densities one to two orders of magnitude lower than in unperturbed microcosms, but their populations increased to densities significantly higher than in unperturbed microscosms 10 to 15 days after inoculation. Predators of bacteria (protozoans, cladocerans, nematodes, and rotifers) were present during the experiment in unperturbed microcosms, while dense populations of bacteriovorous nanoflagellates developed in perturbed microcosms. Preemptive inoculation of perturbed microcosms with GEMs did not have a longlasting effect on the recovery of total, proteolytic, cellulolytic, and pectolytic bacteria in perturbed microscosms, indicating the absence of competitive exclusion.