Evidence for osmotic constraint in F-type bacterial mating

An investigation was made into the relationship between extracellular solute concentration and transfer frequency in F-type mating in Escherichia coli . Solute concentrations above a certain level correlated with a sharp decrease in transfer frequency which was not due to a loss of cell viability; this effect was obtained both with electrolyte (sodium chloride) and with osmotically equivalent non-electrolyte ( myo -inositol), despite the contrasting effects of these solutes at lower concentrations. It is hypothesized that the inhibition of conjugal transfer at high solute concentrations is due to plasmolytic rupture of adhesion sites (“Bayer's junctions”).