Survival of Plasmid-Containing Strains of 'Escherichia coli' in Soil: Effect of Plasmid Size and Nutrients on Survival of Hosts and Maintenance of Plasmids

摘要

Several strains of Escherichia coli, containing plasmids that ranged in size from 3.9 to 96 kb, were inoculated into soil at 10,000 - 100,000 cells/g soil. The initial total bacterial population was approximately 5 x 10 to the 7th power cells/g soil, and the gram-negative bacterial population ranged from 100,000 - 1,000,000 cells/g soil. Changes in various populations were followed on selective media, and as few as 1 to 20 introduced colony forming units (CFU)/g soil could be detected. The decline of the plasmid-containing strains was less rapid than that of the plasmidless hosts in the two host and host-plasmid systems that were compared. The addition of nutrients, initially or during the incubation, resulted in an increase in all bacteria and decreased the rate of decline of introduced strains. The results indicated that the survival of some genetically engineered bacteria in soil is primarily a function of the bacterial strain. No transfer of plasmids to indigenous bacteria was apparent in these studies.