Bacteria Suffer a Bad Reputation, But They Help Make Life Possible

Jun. 10–WASHINGTON — Bacteria suffer a bad reputation. These tiny, one-celled organisms are rightly blamed for hundreds of afflictions from gum disease and strep throat to killers such as cholera and anthrax.

But there’s another side to the bacteria story: We couldn’t live without them.

“They protect us and feed us,” said Abigail Salyers, a bacterial expert at the University of Illinois, Urbana-Champaign, and past president of the American Society for Microbiology. “All life on Earth depends on their activities.”

Scientists keep finding new ways in which bacteria are helpful to animals, plants and almost every creature bigger than a single cell. Researchers described some of their findings at a recent ASM conference in Washington:

–Gemma Reguera of the University of Massachusetts, Amherst, is developing “microbial batteries,” colonies of bacteria that generate electricity from waste organic matter and seafloor sediments. “The Department of Defense is interested in this technology for powering electronic-monitoring devices in remote locations such as the ocean floor,” Reguera said.

–Frank Loeffler, of the Georgia Institute of Technology, Atlanta, has discovered bacteria that can convert toxic substances such as vinyl chloride into harmless fluids. “Such innovative technologies are needed to clean up numerous contaminated aquifers to protect threatened drinking-water reservoirs,” he said.

–Steven Van Gindel of Pennsylvania State University, University Park, uses bacteria to make hydrogen and natural gas from wastewater at food-processing plants. “Once they are introduced into the wastewater, they eat the food in the water and produce hydrogen,” he said. “Then they eat the leftovers and produce methane.”

–Robert Steffan of Envirogen Inc., Lawrenceville, N.J., reported progress in using bacteria to digest and recycle pollutants such as the fuel additive MTBE, methyl tertiary butyl ether.

Bacteria, from a Greek word meaning “rod,” come in an amazing variety of shapes, colors and sizes. Ten million of the smallest ones could form a line 1 inch long. An average teaspoon of soil contains half a billion bacteria. Your mouth is home to 500 different species.

Although many bacteria are rod-shaped, others are tiny spheres, spirals or stringy filaments. Unlike more complex organisms, a bacterial cell lacks a nucleus. Its DNA sprawls loosely inside a jelly-like substance, called cytoplasm, packed inside a stiff cell wall. Bacteria reproduce by dividing, sometimes as rapidly as every 20 minutes.

Scientists have long known about the virtues, as well as the vices, of bacteria. These creatures enable us to digest food and convert it into energy. They produce the oxygen we breathe. They capture nitrogen from the air and fix it in plant roots. They get rid of dead plants and animals. They help make bread and beer.

These bugs are inventive. Some synthesize microscopic chains of magnetic crystals, which let them sense their direction, like a simple compass. Bacteria equipped by nature with miniature oars (called flagella) could be tethered to a fixed spot and used as minuscule pumps in industrial or medical devices, according to Steve Tung, a mechanical engineer at the University of Arkansas, Fayetteville.

Bacteria are tough. Varieties known as “extremophiles” survive below-zero temperatures and 266-degree waters. They scoff at acids and radioactive uranium waste. They thrive in deserts, ice, salt flats and rocks more than a mile below the Earth’s surface. They multiply on the ocean floor without the benefit of sunlight or oxygen.

“Rocks serve as the sole energy source for growth of these bacteria,” said Katrina Edwards of the Woods Hole Oceanographic Institution, Woods Hole, Mass.

NASA tests have shown that bacteria can survive the shock and cold of interplanetary travel. Some are living on the surface of Mars Odyssey, a spaceship that left Earth two years ago and is orbiting Mars.

Some scientists think bacteria are far more likely than complex forms of life to exist on distant planets.

Bacteria are the oldest form of life on Earth, arising when the planet was a few hundred million years old. They ruled the world alone for its first 3 billion years.

“If a space traveler had landed on Earth 1 to 2 billion years ago, that traveler might well have concluded that there was no life on Earth unless he or she had the foresight to bring a microscope,” Salyers said. “These microbes were not only making a living for themselves, but also were making the Earth habitable for plants and animals that appeared much later.”

One of the earliest species, cyanobacteria, is credited with the “oxygen revolution” that transformed the atmosphere of our planet more than 2 billion years ago.

Cyanobacteria are “arguably the most important organisms ever to appear on Earth,” Andrew Knoll, a Harvard University paleontologist, wrote in his new book, “Life on a Young Planet.”"They made breathable air possible.”

These microbes, also known as blue-green bacteria, are still found almost everywhere, commonly in the form of pond scum.

“Many of the cyanobacteria we see today are survivors from the ancient Earth,” Knoll wrote.

In addition to their independent life, cyanobacteria took on a new role as chloroplasts, specialized organs in plant cells that carry out photosynthesis, the process by which green leaves use sunlight to manufacture food and oxygen from water and carbon dioxide in the air.

Plant and animals cells harbor another type of bacteria in miniature factories called mitochondria, which do the vital work of converting food (carbohydrates) into energy.

These bacterial houseguests took up residence in their hosts at least a billion years ago and haven’t worn out their welcome yet.

Knoll pointed out that human beings, in a real sense, are guests in a world shaped for them by bacteria.

“We have evolved to fit in a bacterial world, and not the reverse,” he wrote. “Animals may be evolution’s icing, but bacteria are the cake.”

CLOSER LOOK:

For more information about bacteria on the Web, go to www.microbeworld.org/htm/aboutmicro/microbes/types/bacteria.htm#top

Cyanobacteria have their own Web site: www-cyanosite.bio.purdue.edu

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(c) 2003, Knight Ridder. Distributed by Knight Ridder/Tribune Business News.