The Fifth Miracle: The Search for the Origin and Meaning of Life by Paul Davies

Author:Paul Davies [Davies, Paul]
Language: eng
Format: epub
ISBN: 9780684863092
Amazon: 068486309X
Publisher: Simon & Schuster
Published: 1999-01-01T23:00:00+00:00

CHAPTER 7

Superbugs

IN THE LATE 1920S, the Egyptian capital of Cairo was plagued by a spate of main drain collapses. Investigations revealed that the concrete lining of the sewer pipes had simply disintegrated after as little as two years in the ground. Civil engineers began a series of experiments to determine the cause of the damage. Rapidly crumbling sewers then began to crop up in other places too. In Orange County, California, the twenty-six-mile trunk outfall became badly corroded, and had to be chlorinated to stop the rot; the fifty-five-mile northern outfall in Los Angeles was prevented from total collapse only with the aid of forced ventilation. In South Africa, Cape Town engineers were baffled by galloping corrosion of their concrete sewer pipes, some of which were devoured at the rate of a quarter-inch per year. Clearly something strange was going on below ground.

When the sewers in several Australian towns and cities also began collapsing, the Melbourne and Metropolitan Board of Works were called in. A research project was set up under special investigator Dr. C. D. Parker, who obtained samples of severely affected sewer pipes from around the country. By that stage, engineers already suspected that the problem was somehow associated with hydrogen sulfide—the evil-smelling gas reminiscent of bad eggs—but the sheer speed and virulence of the corrosion was puzzling.

It was not long before Parker discovered what was happening.1 Previous theories focused on some sort of chemical transformation of the concrete, but Parker realized that the corrosion was in fact due to biological attack. He soon isolated the culprit: a slender rod-shaped bacterium about two micrometers long. This bizarre microorganism eats into solid concrete, turning it into a puttylike substance after just a few weeks. Unlike normal organisms that consume organic matter to grow, Parker’s microbes seemed to thrive on a diet of sulfur, which they extracted from the hydrogen-sulfide gas emitted by the sewage. Parker was able to culture the bacteria, and he chose the tentative name Thiobacillus concretivorus, meaning “concrete-eating sulfur rod.”

Laboratory tests revealed that Thiobacillus concretivorus produced sulfuric acid, and it was this that was destroying the concrete sewer pipes. Indeed, the isolated bacteria refused to grow unless they were immersed in sulfuric acid. The concentration of the acid was astonishing, enough to kill all other creatures and even strong enough to dissolve strips of metal! It turned out that Parker’s acid-loving bugs were already known to science; they had been discovered many years earlier and given the name Thiobacillus thio-oxidans. They are one of a number of micro-organisms known as acidophils—acid lovers—that positively demand an acid medium in which to live, and lurk in places like coal and iron-ore dumps. Some of them can tolerate a fluid with a pH as low as 2, which would prove distinctly painful if you were to put your hand in it.

No less remarkable than Thiobacillus thio-oxidans is a tough little microbe called Halobacterium halobium, found where no life is supposed to exist—in the Dead Sea. This inland lake is so salty that bathers can easily sit upright (I once tried it myself).

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