Extremofilos

Extremophiles
These microbes thrive under conditions that would kill other creatures. The molecules that enable extremophiles to prosper are becoming useful to industry
by Michael T. Madigan and Barry L. Marrs
DEEP-SEA VENT

HEAT-LOVING MICROBES (THERMOPHILES AND HYPERTHERMOPHILES) SEA ICE

COLD-LOVING MICROBES (PSYCHROPHILES)

Methanopyrus kandleri

Polaromonas vacuolata

Imagine diving into a refreshingly cool swimming pool. Now, think instead of plowing into water that is boiling or near freezing. Or consider jumping into vinegar, household ammonia or concentrated brine. The leap would be disastrous for a person. Yet many microorganisms make their home in such forbidding environments. These microbes are called extremophiles because they thrive under conditions that,from the human vantage, are clearly extreme. Amazingly, the organisms do not merely tolerate their lot; they do best in their punishing habitats and, in many cases, require one or more extremes in order to reproduce at all. Some extremophiles have been known for more than 40 years. But the search for them has intensified recently, as scientists have recognized that places once assumed to be sterileabound with microbial life. The hunt has also been fueled in the past several years by industry’s realization that the “survival kits” possessed by extremophiles can poten82 Scientific American April 1997

tially serve in an array of applications. Of particular interest are the enzymes (biological catalysts) that help extremophiles to function in brutal circumstances. Like synthetic catalysts,enzymes, which are proteins, speed up chemical reactions without being altered themselves. Last year the biomedical field and other industries worldwide spent more than $2.5 billion on enzymes for applications ranging from the production of sweeteners and “stonewashed” jeans to the genetic identification of criminals and the diagnosis of infectious and genetic diseases. Yet standard enzymes stopworking when exposed to heat or other extremes, and so manufacturers that rely on them must often take special steps to protect the proteins during reactions or storage. By remaining active when other enzymes would fail, enzymes from extremophiles—dubbed “extremozymes”—can potentially eliminate the need for those added steps,
Copyright 1997 Scientific American, Inc.

thereby increasing efficiency andreducing costs. They can also form the basis of entirely new enzyme-based processes. Perhaps 20 research groups in the U.S., Japan, Germany and elsewhere are now actively searching for extremophiles and their enzymes. Although only a few extremozymes have made their way into use thus far, others are sure to follow. As is true of standard enzymes, transforming a newly isolated extremozyme into aviable product for industry can take several years. Studies of extremophiles have also helped redraw the evolutionary tree of life. At one time, dogma held that living creatures could be grouped into two basic domains: bacteria, whose simple cells lack a nucleus, and eukarya, whose cells are more complex. The new work lends strong support to the once heretical proposal that yet a third group, thearchaea, exists. Anatomically, archaeans lack a nucleus and closely resemble bacteria in other ways. And certain archaeal genes have similar counterparts in bacteria, a sign that the two groups function simiExtremophiles

SODA LAKE ALKALI-LOVING MICROBES (ALKALIPHILES)

ACID-LOVING MICROBES (ACIDOPHILES)

SULFURIC SPRING Natronobacterium gregoryi

Haloferax volcanii Sulfolobusacidocaldarius SALT-LOVING MICROBES (HALOPHILES)

PUNISHING ENVIRONMENTS are “home, sweet home” to extremophiles. The microbes shown are examples of the many found in the habitats depicted.

SALT LAKE

larly in some ways. But archaeans also possess genes otherwise found only in eukarya, and a large fraction of archaeal genes appear to be unique. These unshared genes establish archaea’s separate...