Representative plasmids for most incompatibility groups in Escherichia coli K-12 were transferred to a "bald" strain to compare transfer frequencies for liquid and solid media. Standard broth matings were used for a liquid environment, but for solid surface mating, conjugation was allowed to take place on nutrient plates before washing off the cells for transconjugant selection on plates containing appropriate drugs. Plasmids that determine rigid pili transferred at least 2,000X better on plates than in broth. Some plasmids that determine thick flexible pili transferred 45 to 470x better, whereas others transferred equally well in both environments, as did plasmids of the I complex, which determine thin flexible pili. These results clearly distinguished a number of surface mating systems where most plasmids were derepressed for transfer and determined conjugative pili constitutively. The temperature-independent IncH2 plasmid R831b transferred best on plates, but other IncH plasmids transferred equally well in broth. This inconsistency led to the reclassification of R831b as IncM.
An Enterobacter cloacae strain isolated from the faeces of a child with diarrhoea in Indonesia contained a transferable 216 MDa plasmid, pIN32, exhibiting IncHI2 phenotypic characters, including temperature sensitivity of transfer and the expression of H serotype pili at a repressed level. A derivative plasmid (pIN32-1), which had lost the IncHI2 phenotype, and contained only 60 MDa of the original replicon, was obtained after mating at 37 degrees C. It was IncFII, showed regions of homology with plasmid R100, determined IncFII serotype conjugative pili constitutively and was transfer-derepressed. After overnight growth at 37 degrees C in non-selective medium, pIN32 gave rise to another derivative, pIN32-2 (size 184.3 MDa), which retained the IncHI2 phenotype and several other pIN32 characters.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.