The Differential Roles of K⁺, Proline and Betaine in Osmoregulation of Escherichia coli B

Abstract

When Escherichia coli B growing logarithmically in minimal medium was stressed suddenly by 0.5M NaCl, intracellular levels of K⁺ and amino acids (peptides) increased temporarily in that order. But betaine and proline levels were very low and scarcely increased. The increased levels decreased with the resumption of growth. In complex medium, intracellular levels of K⁺, betaine, proline, and other amino acids (peptides) increased in that order; when betaine and proline were present in the medium, the cells accumulated these solutes during stress. The increased levels of K⁺, proline, and other amino acids (peptides) also decreased with the resumption of growth. In contrast with those solutes, betaine level increased continuously and contributed to adjusting the turgor pressure. The cells had the same osmoregulative function regardless of proline level in the cell, and further, osmotolerance under limited K⁺ level declined considerably.