Adapting to Extremes: The Versatility of Oceanic Microbes

[Loren Booda]

Can certain microorganisms exist both on the ocean's surface and in its deepest trenches? How would they adjust between the physical extremes?

 

[Ouabache]

According to this source, there are microbes that can grow under both conditions.

With reference to microbes in the ocean, those at the bottom are under very high atmospheric pressure (700-800 atm) (atm = atmospheres). At sea level we are at 1 atm. In addition to pressure, many of these organisms will experience colder temperatures at depth compared to the surface.

"Barophilic microorganisms grow best at high pressures although they still grow at 1 atm as well."

Evidently they are quite adaptable.

 

[Ouabache]

The same source I referenced, also describes some of the properties (biochemical and cytological) of microorganisms that favor hyperbarometic (high pressure) conditions.

What does pressure mean to a microbe? First of all, pressure tends to decrease the binding capacity of enzymes... The enzymes of extreme barophiles are often folded differently, in a way so that the pressure has less effect on them.

Membranes can also be affected by pressure. The cell wall outer membranes of barophiles tend to have a different protein composition compared to regular microbes. The porins (diffusion channels in membranes) of a barophile can be made up by a specific outer membrane protein. Its production is caused by a specific gene, which is switched on by high pressure.

The cytoplasmic membranes of barotolerant or barophilic organisms tend to have more of certain chemical compounds: (poly)unsaturated fatty acids and phosphatidylglycerol (a phospholipid). When this page was written, scientists thought that these compounds ensure the membrane’s flexibility at high pressure. It's possible that new research has lead to different conclusions ...

I am not aware of specific mechanisms for these microbes to adapt to life near the ocean's surface. In may be simply that their structure and physiology are not impeded at lower pressure.

Here's one physical analogy. Let's assume you change pressure conditions very slowly. If you made a balloon with a thick semipermeable membrane and fill it with water. Under high pressure it will not implode (membrane will not break), due to both the permeability and thickness of the membrane. At low pressure, the balloon will tend to inflate. However because the membrane is semipermeable, any pressure built up inside the membrane can dissipate, and again the balloon will not explode. It has the capability of maintaining its shape at both extreme conditions.

 

[Loren Booda]

Ouabache,

Thanks for your excellent research.

I wonder whether the osmotic (saline) balance is generally different for barophiles than surface cells.

 

[Ouabache]

I am not a physical ocean scientist, so needed to read up on variation of salinity in the world oceans. In doing so, I learned of the thermohaline circulation system. Deep ocean waters are colder and have a higher salinity than warmer surface waters. See http://science.hq.nasa.gov/oceans/physical/SSS.html
Microbes living in the colder deep ocean would need a mechanism for coping with the higher salinity. Those capable of tolerating or thriving in this higher salt environment are called halophiles

"Halophiles concentrate solutes inside their cells to maintain osmotic balance with the external environment." A good diagram and description of this is at reference2

"Facultative" halophiles tolerate higher saline conditions but live quite comfortably under lower saline conditions too. It is likely that those microbes that can live at both the ocean depths and surface waters, are of this type. I don't know the specific mechanisms that allow them to cope under both conditions, perhaps some of our microbiologists can jump in here with their comments.