I have a microbiology question.

When we put bacterial cells in sucrose solution with concentration higher than 0.5M we observe plasmolysis - the cytoplasmic membrane detaches from the cell wall due to water loss in order to balance the osmotic gradient.

If after that we put some lysozyme in the solution, the cells become spherical as they turn into spheroplasts, but they are still alive.

If we put lysozyme in a solution that contains bacterial cells, but no sucrose, they die. So my question is how does sucrose protect cells from lysis?

  • $\begingroup$ What kind of bacteria did you use, gram positive or gram negative? $\endgroup$
    – Chris
    Commented Jul 21, 2014 at 20:48
  • $\begingroup$ Gram positive, Bacillus megaterium. $\endgroup$ Commented Jul 21, 2014 at 21:56
  • $\begingroup$ hemolysis: this term is used with reference to RBCs $\endgroup$
    Commented Jul 22, 2014 at 5:12
  • $\begingroup$ I beg your pardon. What I actually meant to say was plasmolysys, I always mistake those 2 words. $\endgroup$ Commented Jul 23, 2014 at 15:00

1 Answer 1


This is an interesting question and as often, it has been noted by someone before. In this case it has been a researcher named Claes Weibull, who did his research in the 1950s. He noted (as you did) that sucrose has a protective function on the generation of protoplasts from Bacillus megaterium) with lysozyme. He published the following figure (from the first paper below):

enter image description here

He did not really explain the phenomenon, but speculated about protective function of the sugar in solution when the bacterial cell wall is removed. This also works with PEG in solution (see the third paper below). He published a number of papers on this (if you look him up in Pubmed, you will find more articles, but these seem most relevant):

  1. The isolation of protoplasts from Bacillus Megaterium by controlled treatment with lysozyme
  2. Characterization of the protoplasmic constituents of bacillus megaterium.
  3. Osmotic properties of protoplasts of Bacillus megaterium.

It seems also possible to cultivate these protoplasts on agar plates and let them form "normal shaped" bacteria again:


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