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Thermophiles in Kamchatka

Roald Hoffmann

Some Like It Hot

Our group is an international one, nearly all microbiologists here for a small workshop on the enzymology, molecular biology and biochemistry of thermophiles such as live in these springs. A graduate student in the group sticks in a probe with a thermometer, another a piece of pH paper. The water is bubbling up at 95 degrees Celsius. The pH is 1, about 0.1 molar of sulfuric acid. I would not immerse my finger in that water even if it were cool. Two weeks later, far away, a Yellowstone Park employee dies in an accident, stumbling into a similar boiling pool.

Figure 1. Hot hydrothermal poolsClick to Enlarge Image

Now I know what a thermophile likes. The world's record is an organism called Pyrolobus fumarii that flourishes at 113 degrees Celsius (under pressure, at sea bottom). The pools in Kamchatka are not only acidic, but also basic, up to pH 10.5. When I see life rampant under such conditions, or plants growing in what was lava weeks after an eruption, I can't help thinking that the variegated surface of Mars once bore life too.

In the course of the week, I learn a lot about thermophiles. They are some bacteria and mostly Archaea, the third kingdom of life recognized only in recent decades. Most are anaerobic, not requiring (and sometimes damaged by) oxygen. They are the same and not the same. Of course they have membranes and proteins and nucleic acids, all the wondrous molecular machines of the living. But a normal lipid cell wall would decompose at these temperatures, the hydrogen-bonded helices of proteins would unwind, the genes would fragment and not be faithfully reproduced. An acid and hot environment is what people normally use to denature proteins; these creatures love it.

So they are different. Their lipids are linked by sturdier ether groupings instead of esters. Thus bonded, lipid chains span the entire membrane of the cell to form a monolayer wall. The proteins of thermophiles appear to be reinforced by special sequences of amino acids, and have increased ion-pair content buried inside the protein, which, it has been argued, leads to greater intrinsic stability. A better pH environment is maintained inside the cell. Auxiliary cell components, such as polyamines and small basic proteins that resemble histones in eukaryotic chromosomes, seem to stabilize nucleic acids.

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