SURVIVAL AND IMPACT OF GENETICALLY-ENGINEERED PSEUDOMONAS-PUTIDA HARBORING MERCURY RESISTANCE GENE IN AQUATIC MICROCOSMS

The survival of wild-type and genetically engineered Pseudomonas putid a PpY101 that contained a recombinant plasmid pSR134 conferring mercur y resistance were monitored in aquatic microcosms. We used lake, river , and spring water samples. The density of genetically engineered and wild-type P. putida decreased rapidly within 5 days (population change rate k -0.87 approximately -1.00 day-1), then moderately after 5 to 2 8 days (-0.10 approximately -0.14 day-1). The population change rates of genetically engineered and wild-type P. putida were not significant ly different. We studied the important factors affecting the survival of genetically engineered and wild-type P. putida introduced in aquati c microcosms. Visible light exerted an adverse effect on the survival of the two strains. The densities of genetically engineered and wild-t ype P. putida were almost constant until 7 days after inoculation in n atural water filtered with a 0.45-mum membrane filter, or treated with cycloheximide to inhibit the growth of protozoa. These results sugges ted that protozoan predation was one of the most important factors for the survival of two strains. We examined the impact of the addition o f genetically engineered and wild-type P. putida on indigenous bacteri a and protozoa. Inoculation of genetically engineered or wild-type P. putida had no apparent effect on the density of indigenous bacteria. T he density of protozoa increased in microcosms inoculated with genetic ally engineered or wild-type P. putida at 3 days after inoculation, bu t after 5 to 21 days, the density of protozoa decreased to the same le vel as the control microcosms.