Extremophiles

Home , Extremophile, Methanococcus, Methanopyrus, Natronobacterium, Thermus, Thermus aquaticus

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 thereby increasing efficiency and reduc- magine diving into a refreshingly ing costs. They can also form the basis of cool swimming pool. Now, think entirely new enzyme-based processes. I instead of plowing into water that tially serve in an array of applications. Perhaps 20 research groups in the U.S., is boiling or near freezing. Or consider Of particular interest are the enzymes Japan, Germany and elsewhere are now jumping into vinegar, household am- (biological catalysts) that help extremo- actively searching for extremophiles and monia or concentrated brine. The leap philes to function in brutal circumstanc- their enzymes. Although only a few ex- would be disastrous for a person. Yet es. Like synthetic catalysts, enzymes, tremozymes have made their way into many microorganisms make their home which are proteins, speed up chemical use thus far, others are sure to follow. As in such forbidding environments. These reactions without being altered them- is true of standard enzymes, transform- microbes are called extremophiles be- selves. Last year the biomedical field and ing a newly isolated extremozyme into cause they thrive under conditions that, other industries worldwide spent more a viable product for industry can take from the human vantage, are clearly ex- than $2.5 billion on enzymes for appli- several years. treme. Amazingly, the organisms do not cations ranging from the production of Studies of extremophiles have also merely tolerate their lot; they do best in sweeteners and “stonewashed” jeans to helped redraw the evolutionary tree of their punishing habitats and, in many the genetic identification of criminals life. At one time, dogma held that living cases, require one or more extremes in and the diagnosis of infectious and ge- creatures could be grouped into two ba- order to reproduce at all. netic diseases. Yet standard enzymes sic domains: bacteria, whose simple cells Some extremophiles have been known stop working when exposed to heat or lack a nucleus, and eukarya, whose cells for more than 40 years. But the search other extremes, and so manufacturers are more complex. The new work lends for them has intensified recently, as sci- that rely on them must often take spe- strong support to the once heretical pro- entists have recognized that places once cial steps to protect the proteins during posal that yet a third group, the archaea, assumed to be sterile abound with mi- reactions or storage. By remaining ac- exists. Anatomically, archaeans lack a crobial life. The hunt has also been fu- tive when other enzymes would fail, en- nucleus and closely resemble bacteria in eled in the past several years by indus- zymes from extremophiles—dubbed other ways. And certain archaeal genes try’s realization that the “survival kits” “extremozymes”—can potentially elim- have similar counterparts in bacteria, a possessed by extremophiles can poten- inate the need for those added steps, sign that the two groups function simi-

ACID-LOVING MICROBES SULFURIC SPRING (ACIDOPHILES) Natronobacterium gregoryi

Haloferax volcanii Sulfolobus acidocaldarius SALT-LOVING MICROBES (HALOPHILES)

PUNISHING ENVIRONMENTS are SALT LAKE “home, sweet home” to extremophiles. The microbes shown are examples of the many found in the habitats depicted. 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 un- long-term exposure to temperatures shared genes establish archaea’s sepa- higher than about 60 degrees C (140 rate identity. They may also provide new degrees F). an Sulfolobus acidocaldarius, grows O OSTI clues to the evolution of early life on Thermophiles that are content at tem- proliﬁcally at temperatures as high as T OBER

the earth [see box on pages 86 and 87]. peratures up to 60 degrees C have been 85 degrees C. They also showed that R known for a long time, but true extrem- microbes can be present in boiling water. Some Need It Hot ophiles—those able to flourish in greater Brock concluded from the collective heat—were first discovered only about studies that bacteria can function at eat-loving microbes, or thermo- 30 years ago. Thomas D. Brock, now higher temperatures than eukarya, and Hphiles, are among the best studied retired from the University of Wiscon- he predicted that microorganisms would of the extremophiles. Thermophiles re- sin–Madison, and his colleagues uncov- likely be found wherever liquid water produce, or grow, readily in tempera- ered the earliest specimens during a existed. Other work, including research tures greater than 45 degrees Celsius long-term study of microbial life in hot that since the late 1970s has taken sci- (113 degrees Fahrenheit), and some of springs and other waters of Yellowstone entists to more hot springs and to envi- them, referred to as hyperthermophiles, National Park in Wyoming. ronments around deep-sea hydrother- favor temperatures above 80 degrees C The investigators found, to their as- mal vents, has lent strong support to (176 degrees F). Some hyperthermo- tonishment, that even the hottest springs these ideas. Hydrothermal vents, some- philes even thrive in environments hot- supported life. In the late 1960s they times called smokers, are essentially nat- ter than 100 degrees C (212 degrees F), identified the first extremophile capable ural undersea rock chimneys through the boiling point of water at sea level. In of growth at temperatures greater than which erupts superheated, mineral-rich comparison, most garden-variety bacte- 70 degrees C. It was a bacterium, now fluid as hot as 350 degrees C. ria grow fastest in temperatures be- called Thermus aquaticus, that would To date, more than 50 species of hy- tween 25 and 40 degrees C (77 and 104 later make possible the widespread use perthermophiles have been isolated, degrees F). Further, no multicellular an- of a revolutionary technology—the poly- many by Karl O. Stetter and his col- imals or plants have been found to tol- merase chain reaction (PCR). About this leagues at the University of Regensburg erate temperatures above about 50 de- same time, the team found the first hy- in Germany. The most heat-resistant grees C (122 degrees F), and no micro- perthermophile in an extremely hot and of these microbes, Pyrolobus fumarii, bial eukarya yet discovered can tolerate acidic spring. This organism, the archae- grows in the walls of smokers. It repro-

Extremophiles Copyright 1997 Scientific American, Inc. Scientific American April 1997 83 duces best in an environment of about counterparts in structure but appear to merase). Its high tolerance for heat led 105 degrees C and can multiply in tem- contain more of the ionic bonds and to the development of totally automat- peratures of up to 113 degrees C. Re- other internal forces that help to stabi- ed PCR technology. More recently, some markably, it stops growing at tempera- lize all enzymes. users of PCR have replaced the Taq tures below 90 degrees C (194 degrees Whatever the reason for their greater polymerase with Pfu polymerase. This F). It gets too cold! Another hyperther- activity in extreme conditions, enzymes enzyme, isolated from the hyperther- mophile that lives in deep-sea chimneys, derived from thermophilic microbes have mophile Pyrococcus furiosus (“flaming the methane-producing archaean Meth- begun to make impressive inroads in in- fireball”), works best at 100 degrees C. anopyrus, is now drawing much atten- dustry. The most spectacular example is A different heat-loving extremozyme tion because it lies near the root in the Taq polymerase, which derives from T. in commercial use has increased the ef- tree of life; analysis of its genes and ac- aquaticus and is employed widely in ficiency with which compounds called tivities is expected to help clarify how PCR. Invented in the mid-1980s by Kary cyclodextrins are produced from corn- the world’s earliest cells survived. B. Mullis, then at Cetus Corporation, starch. Cyclodextrins help to stabilize PCR is today the basis for the foren- volatile substances (such as flavorings in sic “DNA fingerprinting” that re- foods), to improve the uptake of medi- ceived so much attention during cines by the body, and to reduce bitter-

OCK ness and mask unpleasant . BR odors in foods and medicines.

THOMAS D Others Like It Cold, Acidic, Alkaline

TION old environments are A Cactually more common than hot ones. The oceans,

CE ADMINISTR which maintain an average A temperature of one to three degrees C (34 to 38 degrees

UTICS AND SP F), make up over half the ONA OCK earth’s surface. And vast land . BR areas of the Arctic and Ant-

TIONAL AER arctic are permanently froz- THOMAS D NA en or are unfrozen for only a EXTREME ENVIRONMENTS can also be extremely colorful. Halophiles account for the red- few weeks in summer. Sur- ness in salt collection ponds near San Francisco Bay in California (left), and thermophiles brighten prisingly, the most frigid plac- a hot spring in Yellowstone National Park in Wyoming (right). A glass slide dipped directly into es, like the hottest, support one of Yellowstone’s boiling springs soon revealed the presence of abundant microbial life (top). life, this time in the form of psychrophiles (cold lovers). What is the upper temperature limit the recent O. J. Simpson trials. It is also James T. Staley and his colleagues at for life? Do “super-hyperthermophiles” used extensively in modern biological the University of Washington have capable of growth at 200 or 300 degrees research, in medical diagnosis (such as shown, for example, that microbial com- C exist? No one knows, although cur- for HIV infection) and, increasingly, in munities populate Antarctic sea ice— rent understanding suggests the limit screening for genetic susceptibility to ocean water that remains frozen for will be about 150 degrees C. Above this various diseases, including specific forms much of the year. These communities in- temperature, probably no life-forms of cancer. clude photosynthetic eukarya, notably could prevent dissolution of the chemi- In PCR, an enzyme known as a DNA algae and diatoms, as well as a variety cal bonds that maintain the integrity of polymerase copies repeatedly a snippet of bacteria. One bacterium obtained by DNA and other essential molecules. of DNA, producing an enormous sup- Staley’s group, Polaromonas vacuolata, ply. The process requires the reaction is a prime representative of a psychro- Not Too Hot to Handle mixture to be alternately cycled between phile: its optimal temperature for growth low and high temperatures. When Mul- is four degrees C, and it finds tempera- esearchers interested in how the lis first invented the technique, the poly- tures above 12 degrees C too warm for Rstructure of a molecule influences merases came from microbes that were reproduction. Cold-loving organisms its activity are trying to understand how not thermophilic and so stopped work- have started to interest manufacturers molecules in heat-loving microbes and ing in the hot part of the procedure. who need enzymes that work at refrig- other extremophiles remain functional Technicians had to replenish the en- erator temperatures—such as food pro- under conditions that destroy related zymes manually after each cycle. cessors (whose products often require molecules in organisms adapted to more To solve the problem, in the late 1980s cold temperatures to avoid spoilage), temperate climes. That work is still un- scientists at Cetus plucked T. aquaticus makers of fragrances (which evaporate der way, although it seems that the struc- from a clearinghouse where Brock had at high temperatures) and producers of tural differences need not be dramatic. deposited samples roughly 20 years ear- cold-wash laundry detergents. For instance, several heat-loving extrem- lier. The investigators then isolated the Among the other extremophiles now ozymes resemble their heat-intolerant microbe’s DNA polymerase (Taq poly- under increasing scrutiny are those that

84 Scientific American April 1997 Copyright 1997 Scientific American, Inc. Extremophiles prefer highly acidic or basic conditions larly excited by alkaliphilic enzymes. In carbonate and certain other salts can (acidophiles and alkaliphiles). Most nat- Japan, where industry has embraced release ions that produce alkalinity. Not ural environments on the earth are es- extremozymes with enthusiasm, much surprisingly, microbes in those environ- sentially neutral, having pH values be- of the research into alkaliphilic extrem- ments are adapted to both high alkalin- tween five and nine. Acidophiles thrive ozymes has been spearheaded by Koki ity and high salinity. in the rare habitats having a pH below Horikoshi of the Japan Marine Science Halophiles are able to live in salty five, and alkaliphiles favor habitats with and Technology Center in Yokosuka. conditions through a fascinating adap- a pH above nine. To work effectively, detergents must tation. Because water tends to flow from Highly acidic environments can result be able to cope with stains from food areas of high solute concentration to naturally from geochemical activities and other sources of grease—jobs best areas of lower concentration, a cell sus- (such as the production of sulfurous accomplished by such enzymes as pro- pended in a very salty solution will lose gases in hydrothermal vents and some teases (protein degraders) and lipases water and become dehydrated unless its hot springs) and from the metabolic ac- (grease degraders). Yet laundry deter- cytoplasm contains a higher concentra- tivities of certain acidophiles themselves. gents tend to be highly alkaline and thus tion of salt (or some other solute) than Acidophiles are also found in the debris destructive to standard proteases and li- its environment. Halophiles contend left over from coal mining. Interestingly, pases. Alkaliphilic versions of those en- with this problem by producing large acid-loving extremophiles cannot tolerate great acidity EXTREMOPHILE PROSPECTORS Karl O. Stetter (left) of the University of Regens- inside their cells, where it burg in Germany and James T. Staley (right) of the University of Washington brave the would destroy such impor- elements to find extremophiles in a Yellowstone hot spring and in Antarctic sea ice, re- tant molecules as DNA. They spectively. The psychrophiles in one ice core are evident as a dark band in the inset. survive by keeping the acid ) out. But the defensive mole- t cules that provide this pro- tection, as well as others that aph and inse gr come into contact with the o phot (

environment, must be able to on operate in extreme acidity. Indeed, extremozymes that ashingt are able to work at a pH be- y of W ersit

— niv low one more acidic than U even vinegar or stomach Y ALE

ﬂuids—have been isolated . ST from the cell wall and un- derlying cell membrane of

some acidophiles. TESY OF JAMES T OUR MICHAEL MILSTEIN Potential applications of C acid-tolerant extremozymes range from catalysts for the synthesis of zymes can solve the problem, and sev- amounts of an internal solute or by re- compounds in acidic solution to addi- eral that can operate efﬁciently in heat taining a solute extracted from outside. tives for animal feed, which are intend- or cold are now in use or being devel- For instance, an archaean known as ed to work in the stomachs of animals. oped. Alkaliphilic extremozymes are Halobacterium salinarum concentrates The use of enzymes in feed is already also poised to replace standard enzymes potassium chloride in its interior. As quite popular. The enzymes that are se- wielded to produce the stonewashed might be expected, the enzymes in its lected are ones that microbes normally look in denim fabric. As if they were cytoplasm will function only if a high secrete into the environment to break rocks pounding on denim, certain en- concentration of potassium chloride is food into pieces suitable for ingestion. zymes soften and fade fabric by degrad- present. But proteins in H. salinarum When added to feed, the enzymes im- ing cellulose and releasing dyes. cell structures that are in contact with prove the digestibility of inexpensive the environment require a high concen- grains, thereby avoiding the need for A Briny Existence tration of sodium chloride. more expensive food. The potential applications for salt- Alkaliphiles live in soils laden with he list of extremophiles does not end tolerant enzymes do not leap to mind carbonate and in so-called soda lakes, Tthere. Another remarkable group— as readily as those for certain other ex- such as those found in Egypt, the Rift the halophiles—makes its home in in- tremozymes. Nevertheless, at least one Valley of Africa and the western U.S. tensely saline environments, especially intriguing application is under consid- Above a pH of eight or so, certain mol- natural salt lakes and solar salt evapora- eration. Investigators are exploring in- ecules, notably those made of RNA, tion ponds. The latter are human-made corporating halophilic extremozymes break down. Consequently, alkaliphiles, pools where seawater collects and evap- into procedures used to increase the like acidophiles, maintain neutrality in orates, leaving behind dense concentra- amount of crude extracted from oil wells. their interior, and their extremozymes tions of salt that can be harvested for To create passages through which are located on or near the cell surface and such purposes as melting ice. Some sa- trapped oil can ﬂow into an active well, in external secretions. Detergent mak- line environments are also extremely al- workers pump a mixture of viscous ers in the U.S. and abroad are particu- kaline because weathering of sodium guar gum and sand down the well hole.

); genes sequenced in full. n the summer of 1996 a large collaboration of The sequencing made it possible to compare M. middle Iscientists deciphered the full sequence of units, jannaschii’s total complement of genes with the or nucleotides, in every gene of Methanococcus many genes that have so far been sequenced in jannaschii—a methane-producing extremophile other organisms. Forty-four percent of M. jan-

HIC INSTITUTION ( that thrives at temperatures near 85 degrees Cel- naschii’s genes resemble those in bacteria or eu- AP sius. The results strikingly confirmed the once karya, or both. And consistent with Woese’s ridiculed proposal that life consists of three major scheme, fully 56 percent are completely different evolutionary lineages, not the two that have been from any genes yet described. routinely described in textbooks. That M. jannaschii has characteristics of bacteria and eukarya but also has marked differences sug-

OODS HOLE OCEANOGR The recognized lineages were the bacteria (with ) ); W their simple cells that lack a true nucleus) and the gests that archaea and the other two lineages om op t ( ott

b eukarya (plants, humans and other animals hav- have a common distant ancestor. Partly because ( ing cells that contain a nucleus). By comparing many archaea and some bacteria are adapted to many nstitution er molecules known as ribosomal RNA in many dif- the conditions widely believed to have existed on , G g aphic I the early earth—especially high heat and little or gr ferent organisms, Carl R. Woese and his collabora-

eano no oxygen—a majority of investi-

egensbur tors at the University of Illinois c gators suspect that those two y of R had concluded in 1977 that a ole O ALVIN (top), a scientific submarine, reaches out an arm ersit ds H group of microbes once classified groups appeared first, diverging o (middle) to snag material around a deep-sea vent. Meth- niv o U W as bacteria and called archaebac- anococcus jannaschii, a spherical cell with many flagella, from a common ancestor rela- CH TER teria belonged, in fact, to a sepa- was among its finds in 1982. The diagram on the opposite tively soon after life began. Later, ANA T . STET A rate lineage: the archaea. M. jan- page depicts the three major evolutionary lineages of life. the eukarya split off from the ar- ARL O OD C K R

Then they set off an explosive to frac- tical. Scientists rarely find large quanti- degrading enzymes, they test to see ture surrounding rock and to force the ties of a single species of microbe in na- whether extracts of the cultured cells mixture into the newly formed crevices. ture. A desired organism must be puri- break down selected proteins. If such The guar facilitates the sand’s dispersion fied, usually by isolating single cells, and activity is detected, the researchers turn into the cracks, and the sand props open then grown in laboratory culture. For to standard biochemical methods to iso- the crevices. Before the oil can pass organisms with extreme lifestyles, isola- late the enzymes responsible for the ac- through the crevices, however, the gum tion and large-scale production can tivity and to isolate the genes encoding must be eliminated. If an enzyme that prove both difficult and expensive. the enzymes. They then must hope that degrades guar gum is added just before the genes can be induced to give rise to the mixture is injected into the well- Harvesting Extremozymes their corresponding proteins in a do- head, the guar retains its viscosity long mesticated host. enough to carry the sand into the crev- ortunately, extremozymes can be pro- In the other approach, investigators ices but is then broken down. Fduced through recombinant DNA bypass the need to grow any cultures of At least, that is what happens in the technology without massive culturing of extremophiles. They isolate the DNA ideal case. But oil wells are hot and often the source extremophiles. Genes, which from all living things in a sample of wa- salty places, and so ordinary enzymes consist of DNA, specify the composi- ter, soil or other material from an ex- often stop working prematurely. An ex- tion of the enzymes and other proteins treme environment. Then, using recom- tremozyme that functioned optimally in made by cells; these proteins carry out binant DNA technology once again, high heat and salt would presumably most cellular activities. As long as mi- they deliver random stretches of DNA remain inactive at the relatively cool, crobial prospectors can obtain sample into a domesticated host—ideally one relatively salt-free surface of the well. It genes from extremophiles in nature or insert per host cell—without knowing would then become active gradually as from small laboratory cultures, they can the identities of the genes in those frag- it traveled down the hole, where tem- generally clone those genes and use them ments. Finally, they screen the colonies perature rises steadily with increasing to make the corresponding proteins. that grow out, looking for evidence of depth. The delayed activity would pro- That is, by using the recombinant DNA activity by novel enzymes. If they find vide more time for the sand mixture to technologies, they can insert the genes such evidence, they know that an in- spread through the oil-bearing strata, into ordinary, or “domesticated,” mi- serted gene is responsible and that it will and the tolerance of heat and salt would crobes, which will often use the genes work in the domesticated host. This enable the enzyme to function longer to produce unlimited, pure supplies of method thus avoids many bottlenecks for breaking down the guar. Preliminary the enzymes. in the traditional process. It turns up laboratory tests of this prospect, by Two approaches have been exploited only enzymes that can be manufactured Robert M. Kelly of North Carolina State to identify potentially valuable extrem- readily in tried-and-true hosts. And in- University, have been encouraging. ozymes. The more traditional route re- vestigators can mine the genes for the If the only sources of extremozymes quires scientists to grow at least small enzymes from mixed populations of were large-scale cultures of extremo- cultures of an extremophile obtained microbes without needing to culture philes, widespread industrial applica- from an interesting environment. If the extremophiles that might have trouble tions of these proteins would be imprac- scientists are looking for, say, protein- growing outside their native milieu.

86 Scientific American April 1997 Copyright 1997 Scientific American, Inc. Extremophiles chaea. Further support for this scenario can be seen in the evolu- zymes and other proteins important to cell structure and func- tionary tree itself: hyperthermophilic, oxygen-sensitive organ- tion are made. Many of the unique archaeal genes undoubtedly isms, such as Methanopyrus (archaea) and Aquifex (bacteria), encode novel proteins that may provide insights into how an- branch off close to the root. cient cells survived. And certain of these unusual proteins can Scientists are eager to learn the nature of the genes that are probably be enlisted for developing innovative medicines or to unique to archaea. Genes are the blueprints from which en- perform new tricks in industry. —M.T.M. and B.L.M. ) 7

BACTERIA ARCHAEA EUKARYA all, 199 ENTAMOEBAE e H entic r

ANIMALS P SLIME MOLDS ( PURPLE BACTERIA GRAM-POSITIVE METHANOBACTERIUM HALOBACTERIUM BACTERIA ganisms

THERMOPROTEUS METHANO- FUNGI or o

COCCUS icr THERMOPLASMA CYANOBACTERIA PYRODICTIUM THERMO- y of M PLANTS g COCCUS FLAVOBACTERIA CILIATES iolo ck B o r B

METHANOPYRUS CE:

THERMOTOGA FLAGELLATES

AQUIFEX MICROSPORIDIA DIPLOMONADS UNIVERSAL ANCESTOR JENNIFER C. CHRISTIANSEN; SOUR

Although the microbes of the world gain that property. Devotees of the oth- help to convert enzymes from ordinary are incredibly diverse, scientists rarely er approach, known as directed evolu- microbes into artificial extremozymes. find in them the perfect enzyme for a tion, make more or less random varia- Discovery of extremophiles opens new given task. Therefore, microbiologists tions in the gene encoding a selected en- opportunities for the development of en- at the cutting edge of industrial enzyme zyme and, from those genes, generate zymes having extraordinary catalytic ca- technology have begun to modify ex- thousands of different versions of the pabilities. Yet for any new enzyme to tremozymes, tailoring them to meet enzyme. Then they screen the collection gain commercial acceptance, its makers specific demands. For instance, after to see whether any of the variations has will have to keep down the costs of pro- finding an extremozyme that degrades gained the hoped-for feature. This last duction, for example, by ensuring that proteins fairly efficiently at high tem- strategy is also said to be Edisonian, be- the domesticated microbes used as the peratures, investigators might alter the cause when Thomas Edison sought a extremozyme-producing factory will enzyme so that it functions across a material to serve as a filament for the reliably generate large quantities of the broader range of acidity and salinity. lightbulb, he tried everything available, protein. The difficulties of perfecting Biologists today generally achieve such from bamboo splints to silk threads, and manufacturing techniques, and the re- modifications in either of two ways. chose the one that worked best. luctance of industries to change systems Practitioners of the “rational design” ap- So far most extremozymes in com- that already work reasonably well, could proach first discern the structural basis mercial use are little altered from their slow the entry of new extremozymes into of the property of interest. Next, they original state. But rational design and commerce. It seems inevitable, howev- alter an enzyme’s gene to guarantee Edisonian approaches promise to en- er, that their many advantages will even- that the resulting catalytic protein will hance extremozymes. They may also tually prove irresistible. SA

The Authors Further Reading

MICHAEL T. MADIGAN and BARRY L. MARRS share a par- Enzymes Isolated from Microorganisms That Grow in Ex- ticular interest in photosynthetic bacteria. Madigan received his treme Environments. M.W.W. Adams and R. M. Kelly in Chem- Ph.D. in bacteriology in 1976 under Thomas D. Brock at the Uni- ical and Engineering News, Vol. 73, No. 51, pages 32–42; Decem- versity of Wisconsin–Madison. He is now professor of microbiolo- ber 18, 1995. gy at Southern Illinois University at Carbondale. Madigan’s studies Extremophiles. Special issue of Federation of European Microbi- focus on the biodiversity and metabolic characteristics of photo- ological Societies (FEMS) Microbiology Reviews, Vol. 18, Nos. synthetic bacteria, especially in extreme environments. Marrs re- 2–3; May 1996. ceived his Ph.D. in biology from Case Western Reserve University Hyperthermophiles in the History of Life. K. O. Stetter in in 1968. He then spent several years in academics and industry, re- Evolution of Hydrothermal Ecosystems on Earth (and Mars?). cently as the founding chief executive ofﬁcer of Recombinant Bio- Edited by Gregory R. Bock and Jamie A. Goode. John Wiley & catalysis, which is commercializing enzymes from extremophiles. He Sons, 1996. is currently founder and head of a new company, Photosynthetic Brock Biology of Microorganisms. Eighth edition. Michael T. Harvest, which plans to make use of the chemicals in green plants. Madigan, John M. Martinko and Jack Parker. Prentice Hall, 1997.