Effects of Osmotic Shock on Uptake and Release of Carbohydrates and Amino Acids by E. coli Resting Cells in Seawater and Buffers

Abstract

Summary The effects of osmotic shock on uptake and release of carbohydrates and amino acids by Escherichia coli cells were investigated by osmotically shocking cells grown in non-salted medium with salted buffer or seawater (upward shock), or stressing cells grown in salted medium with low osmotic strength buffer (downward shock). If the upward shock occurred 1 h before the contact with [ 14 C]-substrates, uptake of almost all of them was generally inhibited due to a lowered initial uptake rate. A further decrease in the initial uptake observed in cells treated with seawater could be attributed to the pH of seawater higher than that of the salted buffer. When the upward shock occurred after the contact with substrates, only lactose was significantly released from cells. A downward osmotic shock applied to cells before the contact with substrates generally resulted in low decreases in the uptake, whereas when it occurred after the contact, it induced generally strong release of all tested substrates. The findings of this work suggest that cells shocked by seawater (upward shock) can restore, at least to some extent, their ability to accumulate nutritive substrates and do not release them into the medium. A downward osmotic shock can drain cells of their osmoprotectants and jeopardize survival of enterobacteria entering the marine medium.