Penetration of Pseudomonas aeruginosa by sodium chloride and its relation to the mechanism of optical effects.

When cells of Pseudomonas aeruginosa were suspended in solutions containing increasing concentrations of NaCl, the optical density (OD) of the suspensions measured within 30 sec was found to increase in proportion to the increase in salt concentration. Measurement of intracellular fluid volumes indicated that the volume of the cells decreased roughly in proportion to the increase in salt concentration. After the initial increase in optical density, there was a slow decrease at all concentrations of NaCl tested except the highest, 500 mm. Metabolic inhibitors such as sodium azide and 2,4-dinitrophenol prevented the decrease. Direct analysis showed that the Na(+) and Cl(-) concentrations in the cells were 86 and 77%, respectively, of the concentrations of the ions in the suspending medium after 1 hr. Measurement of the (22)Na space in packed cells showed that Na(+) penetrated the total fluid space in the packed cells. The penetration of (22)Na was not prevented by the presence of metabolic inhibitors or by 500 mm NaCl in the suspending medium. The results indicate that the OD increases produced in suspensions of P. aeruginosa by NaCl are not due to the osmotic action of the salt. The subsequent optical density decreases observed are under metabolic control.