Ultrastructure Studies of Conjugating Escherichia coli

Abstract

THE process of formation of conjugal pairs is an intriguing aspect of the conjugation system of Escherichia coli. The process involves an interaction of surface components, especially F-pili¹. There is also evidence that implicates further surface components^2–4. Several attempts to obtain visual evidence for the nature of the conjugal bond have been reported, including the early use⁵ of negative staining techniques to study conjugation, and later studies with thin sectioning to obtain ultrastructural evidence^6,7. These studies have demonstrated simple associations in pair formation in which the walls have merely been brought into close juxtaposition⁶, and also a more elaborate system in which bridging bubbles apparently arise from the outer cell wall layers of the recipient cells⁷. All these studies have used morphologically distinct donor and recipient cells to improve the recognition of possible conjugal pairs. Our purpose here is to report the observation, in cultures which consist solely of F⁻ cells, of structures similar to those described above, and to suggest some of the limitations of electron microscopy for studies of this type.