Effect of Osmotic Pressure on Growth of Micro Organisms

Basic concept of- Effect of Osmotic Pressure on Growth of Micro Organisms

by Nadim Dinani

Bacterial cells and the media, in which they are suspended, have independent osmotic concentrations – a function of substances in the solution. When a bacterial cell is placed in medium, an osmotic pressure is exerted across the semi permeable membrane that surrounds the cell.

Generally micro organisms grow best in a medium having a slightly lower osmotic concentration than the cell itself. This causes water to flow into the cell, a condition essential for diffusion of nutrient substances and for the maintenance of outward pressure (turgor), when the osmotic concentration of the medium is considerably lower than that of the cell,(a hypotonic medium)), diffusion of water into the cell is excessive, causing increased turgor. Cells not bound by a rigid wall, such as red blood cells, may burst in a medium of this kind – a phenomenon termed as plasmoptysis. In contrast, if the osmotic concentration of the medium exceeds that of the cells, the medium is said to be hypertonic with respect to the cell. In a hypertonic medium, water leaves the cell and the cytoplasmic membrane shrinks away from the rigid cell wall – a condition termed plasmolysis.