by PhilipJ on 7 November 2008
We are remarkably resistant to changes in our surrounding environment. Our bulky bodies allow us to weather extremes of heat and cold, and our skin protects us if we go for a swim in fresh water or salty water. If things get too uncomfortable, we can always get up and walk away, finding a warmer or cooler or drier place. Bacteria don’t have as many options. They are tiny and they are immersed in water, so changes in the environment can pose life-threatening challenges. For instance, if it rains they may be suddenly surrounded by fresh water. This is dangerous because the water seeps into the cell through osmosis and increases the pressure inside. At other times, the bacterium may be shifted suddenly to salty conditions, which pulls water out and dehydrates the cell. Bacteria have methods for resisting these changes, so they can keep a steady, comfortable osmotic pressure inside.
Bacteria control their internal pressure by changing the concentration of molecules inside. If they are placed in salty conditions, they resist dehydration by transporting ions into the cell and by synthesizing more small molecules. However, if they are placed in pure water, they must reduce their inner concentration of ions and small molecules. In that case, they use mechanosensitive channels that open and allow small molecules to leak out. For instance, in laboratory tests, cells that are placed in fresh water rapidly lose more than 95% of small molecules like amino acids, sugars, and potassium ions. However, they keep their proteins or ribosomes safely inside, so they recover quickly and can start up protein synthesis minutes after the conditions return to normal.
Find out more here at the PDB.