Extremophiles are organisms that thrive in extreme environments. For instance some species of bacteria live in the thermal vents of Yellowstone National Park while others live in the polar ice caps. As you might imagine, these bacteria have some rather remarkable differences that enable their survival in their respective environments.

A. Assuming that all membranes are required to be “fluid” for them to function properly, describe differences that you might expect to find in the membrane phospholipids of bacteria from the two extreme environments described above.
B. On an expedition to Antarctica, you “captured” some wild bacteria. (We are all so very proud of you!) Back in the lab, you try to acclimate them to warmer temperatures by slowly raising the temperature of the growth chamber to 25oC over a period of 5 weeks.
B1. What changes in the membrane phospholipids composition would you expect to find?
B2. What changes in the fluid properties of the membrane would you expect to find?
B3. How would you determine if in fact these changes had occurred? Give the results you expect to find.

And your question is?

A. Given that all membranes need to be "fluid" to properly function, the membrane phospholipids of bacteria from extreme environments would be expected to have certain differences in order to adapt to their respective conditions.

1. Thermal Vents: Bacteria living in thermal vents typically experience high temperatures. To maintain the fluidity of their membranes, these bacteria would likely have phospholipids with a higher proportion of unsaturated fatty acids. Unsaturated fatty acids have double bonds in their carbon chains, which introduce kinks and prevent lipid molecules from packing closely together. This results in a more fluid and flexible membrane, allowing the bacteria to survive in the extreme heat.

2. Polar Ice Caps: Bacteria living in polar ice caps face extremely low temperatures. These bacteria would require membranes that remain fluid even in freezing conditions. To achieve this, they might have phospholipids with a higher proportion of saturated fatty acids. Saturated fatty acids have straight carbon chains, which allow lipid molecules to pack tightly together, reducing fluidity. By increasing the proportion of saturated fatty acids, the bacteria can maintain the necessary membrane fluidity in cold temperatures.

B. When attempting to acclimate bacteria from Antarctica to warmer temperatures in the lab, several changes in the membrane phospholipids composition and fluid properties would be expected over time.

B1. Changes in Membrane Phospholipids: As the temperature is gradually raised, the bacteria would likely undergo certain adaptations in their membrane composition. They might increase the proportion of saturated fatty acids in their phospholipids to reduce membrane fluidity and stabilize the membrane structure. This adjustment would allow the bacteria to maintain the necessary fluidity despite the warmer environment.

B2. Changes in Fluid Properties: The overall fluidity of the bacterial membrane would decrease due to the increase in saturated fatty acids. This would result in a membrane that is less flexible and more rigid, compared to the original membrane at low temperatures. The reduced fluidity would enhance membrane stability and prevent leakage of cellular components, which is crucial for the bacteria's survival.

B3. Determining Changes: To determine if these changes in membrane phospholipids have occurred, several approaches can be employed:

- Lipid analysis: The composition of membrane phospholipids can be determined by conducting lipid analysis techniques such as gas chromatography or mass spectrometry. Comparing the lipid profiles of the bacteria before and after the temperature acclimation period will reveal any changes in the proportions of saturated and unsaturated fatty acids.

- Membrane fluidity assays: Fluorescent probes, such as Laurdan or DPH, can be used to assess membrane fluidity. These probes have different fluorescence spectra depending on the fluidity of the surrounding lipid environment. By labeling the bacterial membranes with these probes and measuring the fluorescent signals, one can determine if the acclimation to warmer temperatures has resulted in changes in membrane fluidity.

If the bacterial membranes have indeed undergone the expected changes in their phospholipid composition and fluid properties, the lipid analysis would reveal an increase in saturated fatty acids, while the membrane fluidity assays would indicate a decrease in membrane fluidity compared to the original state.