Transport and Retention of K ⁺ and Other Metabolites in a Marine Pseudomonad and Their Relation to the Mechanism of Optical Effects

Abstract

Suspensions of cells of a marine pseudomonad washed with 0.05 M MgSO4 showed an immediate increase in optical density (first-phase optical change) when the salt concentration of the suspending medium was increased; a subsequent slow decrease in optical density (second-phase optical change) occurred if K+ was present.The rate of the second-phase change was similar to the rate of uptake of 42K+ by the cells. Glutamate increased the rate and extent of the second-phase change and produced a parallel increase in the rate and extent of uptake of 42K+. Citrate inreport presented here concerns the mechanism of the second-phase optical change in suspensions of the marine pseudomonad. 790 on July 31, 2020 by guest http://jb.asm.org/ Downloaded from VoL. 102,1970 K+ AND OPTICAL EFFECTS IN A MARINE PSEUDOMONAD

K + -Dependent Deplasmolysis of a Marine Pseudomonad Plasmolyzed in a Hypotonic Solution

“…Plasmolysis and deplasmolysis in this particular case have been ascribed to the loss and gain, respectively, of K+ by the cells. Optical effects described previously in suspensions of these cells (9,10) have been related to the morphological changes.…”

“…Intracellular potassium determination. The procedures used have been described in a previous communication (10).…”

“…The decreased volume has been ascribed to an interaction of the added salts with electronegative components of the cell envelope, causing the contraction of the latter and shrinkage of the cells. The second-phase change, the slow decrease in OD, was accompanied by an increase in the volume of the cells and was found to require the presence of K+ in the medium (9,10).…”

Osmoregulation and compatible solutes in eubacteria

“…The accumulation of potassium requires the additional accumulation of a corresponding anion, which is thought to be mainly glutamic acid. A correlation was found between the accumulation of potassium and uptake of negatively charged amino acids like glutamic acid or T-aminobutyric acid in response to osmotic stress in several bacteria [31,36,37].…”

“…In E. coli and a number of other bacteria, including some moderate halophiles, the intracellular potassium concentration is highest during the early exponential growth phase, while in the stationary phase potassium concentrations decrease, and internal sodium concentrations (maintained at a low level during active growth) increase [30]. In a number of non-halophilic and marine bacteria, internal potassium concentrations also depend on the osmolarity of the medium [31][32][33][34][35][36][37][38]. When the turgor pressure is reduced by increasing the osmolarity of the medium, the cells shrink and respond to the decreased turgor pressure by initiating potassium uptake, suggesting that osmotic balance and regain of turgor pressure is achieved at least in part by accumulation of potassium from the medium.…”