Carved into a hillside near Butte, Montana, lies the Berkeley Pit, an industrial body of water that stretches about one mile across and contains a volume of close to 30 billion gallons. This small lake was formerly the site of a copper pit mine abandoned in 1982 and left to fill up with water from local springs. Lying at the bottom of the pit was a massive layer of mining waste that had accumulated over many years of mining.

The gradual dissolution of the waste in the water transformed Berkeley Pit into a giant vat of concentrated chemicals so toxic that it was considered uninhabitable to living things. Among the substances found in abundance are heavy metals such as lead, cadmium, aluminum, copper, iron, and zinc, as well as arsenic and sulfides. The pit also has a high level of acidity—10,000 times more than a normal freshwater habitat. The greatest concern is that water from the pit will leak into local streams and contaminate groundwater, river drainages, and eventually the ocean. The Environmental Protection Agency is currently reviewing possible methods of cleaning up the site to avert a possible ecological disaster.

When scientists from the University of Montana began researching the composition of the water in the pit, they were startled by what they found. The samples showed signs of a well-established community of microorganisms that had taken hold over the 20 years the pit lay undisturbed. It included an array of very hardy bacteria, protozoa, fungi, and algae—nearly 50 species in all (see Chapter-opening photo). The microbes evidently entered the pit from the water and air, and rather than being killed, they survived, grew, and spread into available niches.* In a relatively short time, some of them had actually evolved to depend on the toxic sludge for survival. An important observation made by the Montana researchers is that the microbes appear to be naturally detoxifying the water. They are currently investigating a way to adapt this "self-cleaning” technology to clear the system of toxic chemicals and in time convert the lake to a useful water reservoir.

This example should serve as a dramatic reminder of the overwhelming adaptability of microorganisms, which allows them to prevail in environments that would be toxic to all other living things (see Spotlight on Microbiology 7.1, page 190). There are millions of habitats on earth, both of natural and human origin. Microbes are exposed to a tremendous variety in nutrient sources, temperatures, gases, salt, pH, and radiation. With this theme in mind, this chapter will take a closer look at this adaptability in the light of nutrition, responses to environmental factors, transport, and growth.