Effect of substitution of monovalent anions in external medium on the swimming pattern of Salmonella typhimurium.

The effect of replacement of ions in the extracellular medium on the swimming pattern of bacteria (Salmonella typhimurium) has been investigated. The replacement of chloride ion (Cl-) in the standard medium by methanesulfonate ion (MS-) or by propionate ion (Pr-) induced an increase in the tumbling frequency, or a decrease of the end-to-end distances of tracks. Replacement of MS- by Cl- resulted in transient depression of tumbling, and replacement of Pr- by Cl- resulted in immediate recovery of normal swimming. The replacement of cations was not very effective. The experimental data, including the dependence of the effect of replacement on the ion concentration, are consistent with the ideas that the tumbling frequency increases with depolarization of the bacterial membrane and that such anions as MS- and Pr- are more able to permeate the membrane than is Cl-.