How does osmolarity affect bacterial growth?

Question

Vivian Aronson · Accepted Answer

For most bacteria, increasing osmolarity decreases bacterial growth rate. Some bacteria have a preferred osmolarity for maximum growth.

Most bacteria do not need to regulate their internal osmolarity with precision because their cell walls can sustain a considerable osmotic pressure.

The availability of water is the critical factor that affects the growth of cells.

The availability of water is measured by the water activity, #A_"w"#. For pure water, #"A"_"w"# is 1.00.

As the osmolarity increases, the #A_"w"# decreases. Some typical #"A"_"w"# values are

blood, 0.99
seawater, 0.99
maple syrup, 0.90
Great Salt Lake 0.75
The most common solute in nature is salt, #"NaCl"#.

We can classify bacteria according to their growth response to salt.

Nonhalophiles such as E. coli, Pseudomonas and Aquaspirillum serpens cannot tolerate even low levels of osmolarity.

Halotolerant bacteria such as Staphylococcus aureus grow best in the absence of NaCl but can tolerate moderate levels of osmolarity.

Mild Halophiles such as Alteromonas haloplanktis and Pseudomonas marina can tolerate 1-6% salt (sea water is 3% salt).

Moderate Halophiles such as Paracoccus halodenitrificans and Vibrio costicolus grow best in a medium that contains 6-15 % salt.

Extreme Halophiles such as Halococcus morrhuae, Halobacterium salinarium, and Pediococcus halophilus thrive in a medium that contains 15-36 % salt.

From left to right, the graph above shows the growth rate of a nonhalophile, a halotolerant bacterium, and an extreme halophile.

Luna Cruz · Answer

undefined Osmolarity affects bacterial growth by influencing the movement of water across the bacterial cell membrane. High osmolarity environments cause water to move out of the bacterial cell, leading to dehydration and inhibited growth. Conversely, low osmolarity environments can cause excessive water uptake, leading to cell lysis. Bacteria have mechanisms to regulate their internal osmolarity to maintain optimal growth conditions.

Gabriella Anderson · Answer

undefined Osmolarity affects bacterial growth by influencing the movement of water across the bacterial cell membrane. High osmolarity (hypertonic conditions) can cause water to move out of the bacterial cell, leading to shrinkage and potentially inhibiting growth. Low osmolarity (hypotonic conditions) can cause water to enter the cell, potentially leading to cell lysis. Bacteria have mechanisms to regulate osmotic pressure internally to maintain optimal growth conditions.