News Brief 11

 

Microorganisms under extreme conditions:
How do they survive?

 

A mechanical arm of the deep-sea unmanned submersible Kaiko is taking mud samples from the deepest part of the ocean
A mechanical arm of the deep-sea unmanned submersible Kaiko is taking mud samples from the deepest part of the ocean, the Mariana Trench Challenger Deep (10,898m). Kaiko is owned and operated by the Japan Marine Science and Technology Center.

Europa, the ice-covered moon of Jupiter, is the most likely candidate for harboring microbial life in our solar system. More than likely, Europa has an ocean of liquid water beneath its icy crust. If this is indeed the case, could this ocean's environment support some type of primitive life forms? How does life adapt to the high hydrostatic pressure in the ice-covered ocean?

This year the Europa Orbiter will leave Earth with the goal of finding out if Europa does indeed have an ocean. If the result is positive, then a future mission might send some type of robotic submarine to melt through the ice and explore the sea below.

To learn more about how primitive life forms survive under such extreme conditions, two researchers, Dr. Jiasong Fang of Iowa State University and Dr. Tonya Peeples of the University of Iowa, are studying how microorganisms called piezophiles, which live at high-pressure conditions on Earth, adapt to deep-sea low-temperature and high-pressure environments. Their samples for the study are from the Mariana Trench, a depression in the floor of the western Pacific Ocean, just east of the Mariana Islands. The bottom of the Mariana Trench is the deepest known point on Earth.

The researchers are beginning the second year of the study with the assistance of a cooperative grant from the Iowa Space Grant Consortium. Specifically, they are examining lipid components, which are part of the cell membrane, to see how the cells adapt. These components can become solid (the gel state) when the temperature decreases and the pressure increases; for growth to occur, a cell membrane must be in a fluid state (the liquid crystalline state).

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A piezophilic bacterium.A piezophilic bacterium. The bar in the lower left-hand corner is one micron (one millionth of a meter). Electron micrograph, negative image, provided by Dr. Kato at Japan Marine Science and Technology Center.

The lipid components of piezophiles are different from those of bacteria that grow at Earth's surface. Piezophiles can do what surface bacteria cannot do--survive at great depth and great pressure. On the other hand, they can't survive at the surface because they require high pressure to grow.

The mechanisms that piezophiles use to respond biochemically to an extreme environment are poorly understood. One possibility is that the biosynthesis of polyunsaturated fatty acids in the lipids may help piezophiles adapt to the permanent cold and pressurized environment, but evidence confirming that these fatty acids are indeed required to maintain the cell membrane fluidity for growth under high-pressure conditions is lacking.

To explore this idea, the researchers designed and assembled a high-pressure bioreactor system for cultivating piezophilic bacteria at high hydrostatic pressures at various temperatures. They analyzed the fatty acid composition in the lipids of various strains of piezophiles, ranging from piezotolerant to extremely piezophilic bacteria (piezo- is a prefix meaning "pressure").

In the second year of the study, the researchers will try to determine if membrane fluidity correlates with lipid components, thus providing some of the evidence demonstrating that fatty acids are required to maintain cell membrane fluidity under high-pressure conditions.

By studying the adaptation mechanisms of piezophilic bacteria, Fang and Peeples hope to shed light on the possibility of extremophiles (microorganisms that live under extreme conditions) on other planets and on the origin of life on Earth. Studying cell membrane lipids will provide the first line of evidence that life existed or exists on other planets or planetary satellites.

"If we can find an environment on Earth similar to that on other planets," explained Fang, "we will have a better understanding of how life can survive in that environment."