Osmotic Pressure in Microorganisms

Study Notes

Microbial cells typically have higher solute concentrations compared to their natural environments, which are often hypoosmotic.
Rigid cell walls prevent cell lysis by protecting the cells from bursting in dilute environments.
High osmotic pressure can lead to water loss from cells, causing shrinkage (plasmolysis) and potential cell death.
Salt is effective for food preservation, as it helps create an environment unfavorable for microbial growth (e.g., brining meat and fish).
Halophiles require elevated salt concentrations for growth, often found in marine environments with around 3.5% salt.
Extreme halophiles, such as Dunaliella salina and Halobacterium, can thrive in saline lakes 3.5–10 times saltier than ocean water.
Dunaliella salina adapts to high salinity by using glycerol and actively pumping out excess salt.
Halobacterium survives by accumulating potassium and other ions, making proteins that function optimally at high salt concentrations.
Halotolerant organisms can withstand high salt levels but do not need it for growth. Notable examples include Staphylococcus aureus, Bacillus cereus, and Vibrio cholerae, which are associated with foodborne illnesses.

Water activity is crucial for microbial growth, with pure water having an aw of 1.0.
Bacteria primarily thrive in environments with high aw (0.97–0.99), while fungi can grow in drier conditions (e.g., Aspergillus spp. can grow at 0.8–0.75).
Techniques such as drying, freeze-drying, or using brine effectively reduce water content in food, thus preventing spoilage.

Barophiles are microorganisms that thrive under high atmospheric pressure, commonly found at the ocean's bottom.
These organisms are not well understood due to difficulties in studying them in laboratory settings.

Photoautotrophs (e.g., cyanobacteria, green sulfur bacteria) and photoheterotrophs (e.g., purple nonsulfur bacteria) require light for growth.
They harness light energy through pigments to convert it into chemical energy for processes like carbon fixation.
Photosynthetically active radiation (PAR) is the range of light they utilize, measuring from 400 to 700 nanometers (nm) in the visible spectrum, extending into the near-infrared for some.
Accessory pigments, such as fucoxanthin in brown algae and phycobilins in cyanobacteria, enhance light absorption, especially in deeper water environments.