Motility, diffusion and cell concentration affect pair formation in Escherichia coli

Abstract

AT the high cell densities normally used in E.coli matings (about 10⁸ cells per ml) individual cells undergo frequent and repeated collisions, and should therefore have multiple opportunities for pairing^1–3. A mating pair of cells, once formed, will similarly continue to collide almost as frequently with other cells. It is not known whether these secondary collisions affect either the speed or extent of DNA transfer, since the true properties of a mating pair of cells formed with little likelihood of further collisions have not been studied. Pairs formed at low cell concentrations, however, should be suitable for such studies; indeed, they could be regarded as paradigms of simple cell–cell interactions. We show here that at low densities pair formation is much more efficient than at high densities, and also that motility decreases this efficiency once cells have collided.