INFLUENCE OF A SURVIVAL PROCESS IN A FRESH-WATER SYSTEM UPON PLASMID TRANSFER BETWEEN ESCHERICHIA-COLI STRAINS

Survival and potential ability to act as recipient or donor during the survival process for one plasmid-free and four plasmid-bearing Escher ichia coli strains under nonilluminated and illuminated conditions in freshwater systems were studied. The five E. coli strains showed the s ame behavior with respect to the microbial parameters used to characte rize the survival process (culturability and viability). Under nonillu minated conditions, recipient cells did not show variation in the abil ity to receive and express plasmid material, while the culturability o f the recipient strain remained stable. Under the same conditions, don or cells lost their ability for plasmid transfer during the survival p rocess, in all cases more than a 90% decrease of the number of transco njugants was found after 4 days of experimentation, although viable an d culturable cells of donor strains maintained the capacity to express some plasmidic genes. Under illuminated conditions, transconjugants w ere not detected after 2 days of experimentation. The number of transc onjugants formed was dependent not only on the time donor strains rema ined in the water but also on the temperature (20 or 37 degrees C) at which the mating assays were conducted.