CONJUGATIVE PLASMIDS ISOLATED FROM BACTERIA IN MARINE ENVIRONMENTS SHOW VARIOUS DEGREES OF HOMOLOGY TO EACH OTHER AND ARE NOT CLOSELY-RELATED TO WELL-CHARACTERIZED PLASMIDS

Mercury resistance plasmids were exogenously isolated, i.e., recovered after transfer to a model recipient bacterium, from marine air-water interface, bulk water, and biofilm communities during incubation in ar tificial seawater without added nutrients. Ninety-five plasmids from d ifferent environments were classified by restriction endonuclease dige stion, and 12 different structural plasmid groups were revealed. The p lasmid types isolated from different habitats and from different sampl ing occasions showed little similarity to each other based on their re striction endonuclease patterns, indicating high variation and possibl y a low transfer between microhabitats and/or a different composition of the microbial communities at different sites and times. With anothe r approach in which probes derived from one of the isolated plasmids a nd a mercury resistance (mer) probe from Tn501 were used, similarities between plasmids from several different groups were found. The plasmi ds were further tested for their incompatibility by use of the collect ion of inc/rep probes (B/O, com9, FI, FII, HI1, HI2, I1, L/M, N, P, Q, U, W, Y) described by Couturier et al. (M. F. Couturier, P. Bex, L. B ergquist, and W. K. Maas, Microbiol. Rev. 52:375-395, 1988). Hybridiza tions did not reveal any identity between the 12 plasmid groups and an y of the inc/rep probes tested. The results indicate that plasmids iso lated from different marine habitats have replication and/or incompati bility systems that are different from the well-characterized plasmids that are commonly used in plasmid biology. This shows the need for th e use of more relevant plasmids in studies of plasmid activity in the environment and development of new inc/rep probes for their characteri zation.