Microbiology: Principles and Explorations 9th Edition
You’ll Die in 30 Minutes Here!
What’s a Microbiologist Doing Here?
Come with geomicrobiologist Dr. Penny Boston, deep under the Chihuahuan Desert of Mexico, to a cave full of giant gypsum crystals weighting over 5 tons each. A pump has drained out the scalding hot water in which they were immersed for over 100 million years. The cave sits atop a chamber of volcanic magma which heats it to 50°C (120°F) and 99% humidity. Even with special suits, breathing apparatus and ice packs, a human can survive here for less than 30 minutes. But Penny Boston has found over 80 kinds of bacteria living inside fluid in the crystals. All never seen on earth before. She has done their DNA and they are unique. Each drop of fluid also holds over 200 million bacteriophages, a type of virus that eats bacteria! As the crystals grew, defects in their latticework of molecules left small holes which filled with the water bathing them—hot and full of microbes. Further growth closed these holes, preserving the bacteria and viruses alive in the fluid. Most of them are still alive! They are living fossils over a half million years old! They are not dormant. They have a superslow metabolism, extra food just kills them. Red colored bacteria growing on the 80–85 billion year old limestone walls of the cave are also alive. These microbes are living in what is called the “deep hot biosphere,” like what much of the early earth was like.
We Are the Planet of Bacteria
The full extent and importance of bacteria to our planet is just now being revealed. Deep drilling projects have discovered bacteria living at depths that no one had believed possible. At first their presence was attributed to contaminated drilling materials from the surface. But now several careful studies have confirmed populations of bacteria truly native to depths such as 1.6 km in France, 4.2 km in Alaska, and 5.2 km in Sweden. It seems that no matter how far down we drill, we always find bacteria living there. But, as we approach the hot interior of the Earth, temperature increases with depth. The Alaskan bacteria were living at 110°C! Evidence has accumulated that there is a “deep hot biosphere,” as named by American scientist Thomas Gold. This region of microbial life may extend down as far as 10 km below our “surface biosphere.” At places along the border between these
two biospheres, materials such as oil, hydrogen sulfide (H2S), and methane (CH4) are upwelling, carrying along with them bacteria from deep inside our planet. Scientists now speak of a “continuous subcrustal culture” of bacteria filling a deep hot zone lying beneath the entire Earth’s surface. The mass of bacteria in the surface biosphere by far exceeds the total weight of all other living things. Add to this the weight of all the bacteria living inside the deep hot biosphere, and it is apparent that our Earth is truly “the planet of bacteria.”
The cave shown in the photo at the beginning of this chapter is one of those places along the border between the two biospheres. In this book we will examine bacteria at other borderland sites (for example, black hot smoking vents located deep at the ocean bottom; cold seeps higher up in the ocean on the continental shelves; and boiling mud pots such as those at Yellowstone National Park in the United States and at the Kamchatka peninsula of Russia). And, of course, we will take a closer look at those fascinating caves shown at the beginning of this chapter.
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