EFFECTS OF OSMOTIC SHOCK ON UPTAKE AND RELEASE OF CARBOHYDRATES AND AMINO-ACIDS BY ESCHERICHIA-COLI RESTING CELLS IN SEAWATER AND BUFFERS

The effects of osmotic shock on uptake and release of carbohydrates an d amino acids by Escherichia coli cells were investigated by osmotical ly shocking cells grown in non-salted medium with salted buffer or sea water (upward shock), or stressing cells grown in salted medium with l ow osmotic strength buffer (downward shock). If the upward shock occur red 1 h before the contact with [C-14]-substrates, uptake of almost al l of them was generally inhibited due to a lowered initial uptake rate . A further decrease in the initial uptake observed in cells treated w ith seawater could be attributed to the pH of seawater higher than tha t of the salted buffer. When the upward shock occurred after the conta ct with substrates, only lactose was significantly released from cells . A downward osmotic shock applied to cells before the contact with su bstrates generally resulted in low decreases in the uptake, whereas wh en 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 exte nt, their ability to accumulate nutritive substrates and do not releas e them into the medium. A downward osmotic shock can drain cells of th eir osmoprotectants and jeopardize survival of enterobacteria entering the marine medium.