Extremophiles

Imagine diving into a refreshinglycool swimming pool. Now, thinkinstead of plowing into water thatis boiling or near freezing. Or considerjumping into vinegar, household am-monia or concentrated brine. The leapwould be disastrous for a person. Yetmany microorganisms make their homein such forbidding environments. Thesemicrobes are called extremophiles be-cause they thrive under conditions that,from the human vantage, are clearly ex-treme. Amazingly, the organisms do notmerely tolerate their lot; they do best intheir punishing habitats and, in manycases, require one or more extremes inorder to reproduce at all.

Some extremophiles have been knownfor more than 40 years. But the searchfor them has intensified recently, as sci-entists have recognized that places onceassumed to be sterile abound with mi-crobial life. The hunt has also been fu-eled in the past several years by indus-trys realization that the survival kitspossessed by extremophiles can poten-

tially serve in an array of applications.Of particular interest are the enzymes

(biological catalysts) that help extremo-philes to function in brutal circumstanc-es. Like synthetic catalysts, enzymes,which are proteins, speed up chemicalreactions without being altered them-selves. Last year the biomedical field andother industries worldwide spent morethan $2.5 billion on enzymes for appli-cations ranging from the production ofsweeteners and stonewashed jeans tothe genetic identification of criminalsand the diagnosis of infectious and ge-netic diseases. Yet standard enzymesstop working when exposed to heat orother extremes, and so manufacturersthat rely on them must often take spe-cial steps to protect the proteins duringreactions or storage. By remaining ac-tive when other enzymes would fail, en-zymes from extremophilesdubbedextremozymescan potentially elim-inate the need for those added steps,

thereby increasing efficiency and reduc-ing costs. They can also form the basis ofentirely new enzyme-based processes.

Perhaps 20 research groups in the U.S.,Japan, Germany and elsewhere are nowactively searching for extremophiles andtheir enzymes. Although only a few ex-tremozymes have made their way intouse thus far, others are sure to follow. Asis true of standard enzymes, transform-ing a newly isolated extremozyme intoa viable product for industry can takeseveral years.

Studies of extremophiles have alsohelped redraw the evolutionary tree oflife. At one time, dogma held that livingcreatures could be grouped into two ba-sic domains: bacteria, whose simple cellslack a nucleus, and eukarya, whose cellsare more complex. The new work lendsstrong support to the once heretical pro-posal that yet a third group, the archaea,exists. Anatomically, archaeans lack anucleus and closely resemble bacteria inother ways. And certain archaeal geneshave similar counterparts in bacteria, asign that the two groups function simi-

82 Scientific American April 1997 Extremophiles

ExtremophilesThese 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

SEA ICE

COLD-LOVING MICROBES(PSYCHROPHILES)

DEEP-SEAVENT

HEAT-LOVING MICROBES(THERMOPHILES AND

HYPERTHERMOPHILES)

Polaromonas vacuolata

Methanopyruskandleri

Copyright 1997 Scientific American, Inc.

larly in some ways. But archaeans alsopossess genes otherwise found only ineukarya, and a large fraction of archae-al genes appear to be unique. These un-shared genes establish archaeas sepa-rate identity. They may also provide newclues to the evolution of early life onthe earth [see box on pages 86 and 87].

Some Need It Hot

Heat-loving microbes, or thermo-philes, are among the best studiedof the extremophiles. Thermophiles re-produce, or grow, readily in tempera-tures greater than 45 degrees Celsius(113 degrees Fahrenheit), and some ofthem, referred to as hyperthermophiles,favor temperatures above 80 degrees C(176 degrees F). Some hyperthermo-philes even thrive in environments hot-ter than 100 degrees C (212 degrees F),the boiling point of water at sea level. Incomparison, most garden-variety bacte-ria grow fastest in temperatures be-tween 25 and 40 degrees C (77 and 104degrees F). Further, no multicellular an-imals or plants have been found to tol-erate temperatures above about 50 de-grees C (122 degrees F), and no micro-bial eukarya yet discovered can tolerate

long-term exposure to temperatureshigher than about 60 degrees C (140degrees F).

Thermophiles that are content at tem-peratures up to 60 degrees C have beenknown for a long time, but true extrem-ophilesthose able to flourish in greaterheatwere first discovered only about30 years ago. Thomas D. Brock, nowretired from the University of Wiscon-sinMadison, and his colleagues uncov-ered the earliest specimens during along-term study of microbial life in hotsprings and other waters of YellowstoneNational Park in Wyoming.

The investigators found, to their as-tonishment, that even the hottest springssupported life. In the late 1960s theyidentified the first extremophile capableof growth at temperatures greater than70 degrees C. It was a bacterium, nowcalled Thermus aquaticus, that wouldlater make possible the widespread useof a revolutionary technologythe poly-merase chain reaction (PCR). About thissame time, the team found the first hy-perthermophile in an extremely hot andacidic spring. This organism, the archae-

an Sulfolobus acidocaldarius, growsprolifically at temperatures as high as85 degrees C. They also showed thatmicrobes can be present in boiling water.

Brock concluded from the collectivestudies that bacteria can function athigher temperatures than eukarya, andhe predicted that microorganisms wouldlikely be found wherever liquid waterexisted. Other work, including researchthat since the late 1970s has taken sci-entists to more hot springs and to envi-ronments around deep-sea hydrother-mal vents, has lent strong support tothese ideas. Hydrothermal vents, some-times called smokers, are essentially nat-ural undersea rock chimneys throughwhich erupts superheated, mineral-richfluid as hot as 350 degrees C.

To date, more than 50 species of hy-perthermophiles have been isolated,many by Karl O. Stetter and his col-leagues at the University of Regensburgin Germany. The most heat-resistant of these microbes, Pyrolobus fumarii,grows in the walls of smokers. It repro-

Extremophiles Scientific American April 1997 83

PUNISHING ENVIRONMENTS arehome, sweet home to extremophiles.The microbes shown are examples of themany found in the habitats depicted.

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SALT-LOVING MICROBES(HALOPHILES)

SALT LAKE

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Copyright 1997 Scientific American, Inc.

duces best in an environment of about105 degrees C and can multiply in tem-peratures of up to 113 degrees C. Re-markably, it stops growing at tempera-tures below 90 degrees C (194 degreesF). It gets too cold! Another hyperther-mophile that lives in deep-sea chimneys,the methane-producing archaean Meth-anopyrus, is now drawing much atten-tion because it lies near the root in thetree of life; analysis of its genes and ac-tivities is expected to help clarify howthe worlds earliest cells survived.

What is the upper temperature limitfor life? Do super-hyperthermophilescapable of growth at 200 or 300 degreesC exist? No one knows, although cur-rent understanding suggests the limitwill be about 150 degrees C. Above thistemperature, probably no life-formscould prevent dissolution of the chemi-cal bonds that maintain the integrity ofDNA and other essential molecules.

Not Too Hot to Handle

Researchers interested in how thestructure of a molecule influencesits activity are trying to understand howmolecules in heat-loving microbes andother extremophiles remain functionalunder conditions that destroy relatedmolecules in organisms adapted to moretemperate climes. That work is still un-der way, although it seems that the struc-tural differences need not be dramatic.For instance, several heat-loving extrem-ozymes resemble their heat-intolerant

counterparts in structure but appear tocontain more of the ionic bonds andother internal forces that help to stabi-lize all enzymes.

Whatever the reason for their greateractivity in extreme conditions, enzymesderived from thermophilic microbes havebegun to make impressive inroads in in-dustry. The most spectacular example isTaq polymerase, which derives from T.aquaticus and is employed widely inPCR. Invented in the mid-1980s by KaryB. Mullis, then at Cetus Corporation,

PCR is today the basis for the foren-sic DNA fingerprinting that re-ceived so much attention during

the recent O. J. Simpson trials. It is alsoused extensively in modern biologicalresearch, in medical diagnosis (such asfor HIV infection) and, increasingly, inscreening for genetic susceptibility tovarious diseases, including specific formsof cancer.

In PCR, an enzyme known as a DNApolymerase copies repeatedly a snippetof DNA, producing an enormous sup-ply. The process requires the reactionmixture to be alternately cycled betweenlow and high temperatures. When Mul-lis first invented the technique, the poly-merases came from microbes that werenot thermophilic and so stopped work-ing in the hot part of the procedure.Technicians had to replenish the en-zymes manually after each cycle.

To solve the problem, in the late 1980sscientists at Cetus plucked T. aquaticusfrom a clearinghouse where Brock haddeposited samples roughly 20 years ear-lier. The investigators then isolated themicrobes DNA polymerase (Taq poly-

merase). Its high tolerance for heat ledto the development of totally automat-ed PCR technology. More recently, someusers of PCR have replaced the Taqpolymerase with Pfu polymerase. Thisenzyme, isolated from the hyperther-mophile Pyrococcus furiosus (flamingfireball), works best at 100 degrees C.

A different heat-loving extremozymein commercial use has increased the ef-ficiency with which compounds calledcyclodextrins are produced from corn-starch. Cyclodextrins help to stabilizevolatile substances (such as flavorings infoods), to improve the uptake of medi-cines by the body, and to reduce bitter-

ness and mask unpleasantodors in foods and medicines.

Others Like It Cold, Acidic, Alkaline

Cold environments areactually more commonthan hot ones. The oceans,which maintain an averagetemperature of one to threedegrees C (34 to 38 degreesF), make up over half theearths surface. And vast landareas of the Arctic and Ant-arctic are permanently froz-en or are unfrozen for only afew weeks in summer. Sur-prisingly, the most frigid plac-es, like the hottest, supportlife, this time in the form ofpsychrophiles (cold lovers).

James T. Staley and his colleagues atthe University of Washington haveshown, for example, that microbial com-munities populate Antarctic sea iceocean water that remains frozen formuch of the year. These communities in-clude photosynthetic eukarya, notablyalgae and diatoms, as well as a varietyof bacteria. One bacterium obtained byStaleys group, Polaromonas vacuolata,is a prime representative of a psychro-phile: its optimal temperature for growthis four degrees C, and it finds tempera-tures above 12 degrees C too warm forreproduction. Cold-loving organismshave started to interest manufacturerswho need enzymes that work at refrig-erator temperaturessuch as food pro-cessors (whose products often requirecold temperatures to avoid spoilage),makers of fragrances (which evaporateat high temperatures) and producers ofcold-wash laundry detergents.

Among the other extremophiles nowunder increasing scrutiny are those that

Extremophiles84 Scientific American April 1997

EXTREME ENVIRONMENTS can also be extremely colorful. Halophiles account for the red-ness in salt collection ponds near San Francisco Bay in California (left), and thermophiles brightena hot spring in Yellowstone National Park in Wyoming (right). A glass slide dipped directly intoone of Yellowstones boiling springs soon revealed the presence of abundant microbial life (top).

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prefer highly acidic or basic conditions(acidophiles and alkaliphiles). Most nat-ural environments on the earth are es-sentially neutral, having pH values be-tween five and nine. Acidophiles thrivein the rare habitats having a pH belowfive, and alkaliphiles favor habitats witha pH above nine.

Highly acidic environments can resultnaturally from geochemical activities(such as the production of sulfurousgases in hydrothermal vents and somehot springs) and from the metabolic ac-tivities of certain acidophiles themselves.Acidophiles are also found in the debrisleft over from coal mining. Interestingly,acid-loving extremophilescannot tolerate great acidityinside their cells, where itwould destroy such impor-tant molecules as DNA. Theysurvive by keeping the acidout. But the defensive mole-cules that provide this pro-tection, as well as others thatcome into contact with theenvironment, must be able tooperate in extreme acidity.Indeed, extremozymes thatare able to work at a pH be-low onemore acidic thaneven vinegar or stomachfluidshave been isolatedfrom the cell wall and un-derlying cell membrane ofsome acidophiles.

Potential applications ofacid-tolerant extremozymesrange from catalysts for the synthesis ofcompounds in acidic solution to addi-tives for animal feed, which are intend-ed to work in the stomachs of animals.The use of enzymes in feed is alreadyquite popular. The enzymes that are se-lected are ones that microbes normallysecrete into the environment to breakfood into pieces suitable for ingestion.When added to feed, the enzymes im-prove the digestibility of inexpensivegrains, thereby avoiding the need formore expensive food.

Alkaliphiles live in soils laden withcarbonate and in so-called soda lakes,such as those found in Egypt, the RiftValley of Africa and the western U.S.Above a pH of eight or so, certain mol-ecules, notably those made of RNA,break down. Consequently, alkaliphiles,like acidophiles, maintain neutrality intheir interior, and their extremozymesare located on or near the cell surface andin external secretions. Detergent mak-ers in the U.S. and abroad are particu-

larly excited by alkaliphilic enzymes. InJapan, where industry has embracedextremozymes with enthusiasm, muchof the research into alkaliphilic extrem-ozymes has been spearheaded by KokiHorikoshi of the Japan Marine Scienceand Technology Center in Yokosuka.

To work effectively, detergents mustbe able to cope with stains from foodand other sources of greasejobs bestaccomplished by such enzymes as pro-teases (protein degraders) and lipases(grease degraders). Yet laundry deter-gents tend to be highly alkaline and thusdestructive to standard proteases and li-pases. Alkaliphilic versions of those en-

zymes can solve the problem, and sev-eral that can operate efficiently in heator cold are now in use or being devel-oped. Alkaliphilic extremozymes arealso poised to replace standard enzymeswielded to produce the stonewashedlook in denim fabric. As if they wererocks pounding on denim, certain en-zymes soften and fade fabric by degrad-ing cellulose and releasing dyes.

A Briny Existence

The list of extremophiles does not endthere. Another remarkable groupthe halophilesmakes its home in in-tensely saline environments, especiallynatural salt lakes and solar salt evapora-tion ponds. The latter are human-madepools where seawater collects and evap-orates, leaving behind dense concentra-tions of salt that can be harvested forsuch purposes as melting ice. Some sa-line environments are also extremely al-kaline because weathering of sodium

carbonate and certain other salts canrelease ions that produce alkalinity. Notsurprisingly, microbes in those environ-ments are adapted to both high alkalin-ity and high salinity.

Halophiles are able to live in saltyconditions through a fascinating adap-tation. Because water tends to flow fromareas of high solute concentration toareas of lower concentration, a cell sus-pended in a very salty solution will losewater and become dehydrated unless itscytoplasm contains a higher concentra-tion of salt (or some other solute) thanits environment. Halophiles contendwith this problem by producing large

amounts of an internal solute or by re-taining a solute extracted from outside.For instance, an archaean known asHalobacterium salinarum concentratespotassium chloride in its interior. Asmight be expected, the enzymes in itscytoplasm will function only if a highconcentration of potassium chloride ispresent. But proteins in H. salinarumcell structures that are in contact withthe environment require a high concen-tration of sodium chloride.

The potential applications for salt-tolerant enzymes do not leap to mindas readily as those for certain other ex-tremozymes. Nevertheless, at least oneintriguing application is under consid-eration. Investigators are exploring in-corporating halophilic extremozymesinto procedures used to increase theamount of crude extracted from oil wells.

To create passages through whichtrapped oil can flow into an active well,workers pump a mixture of viscousguar gum and sand down the well hole.

Extremophiles Scientific American April 1997 85

EXTREMOPHILE PROSPECTORS Karl O. Stetter (left) of the University of Regens-burg in Germany and James T. Staley (right) of the University of Washington brave theelements to find extremophiles in a Yellowstone hot spring and in Antarctic sea ice, re-spectively. The psychrophiles in one ice core are evident as a dark band in the inset.

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Then they set off an explosive to frac-ture surrounding rock and to force themixture into the newly formed crevices.The guar facilitates the sands dispersioninto the cracks, and the sand props openthe crevices. Before the oil can passthrough the crevices, however, the gummust be eliminated. If an enzyme thatdegrades guar gum is added just beforethe mixture is injected into the well-head, the guar retains its viscosity longenough to carry the sand into the crev-ices but is then broken down.

At least, that is what happens in theideal case. But oil wells are hot and oftensalty places, and so ordinary enzymesoften stop working prematurely. An ex-tremozyme that functioned optimally inhigh heat and salt would presumablyremain inactive at the relatively cool,relatively salt-free surface of the well. Itwould then become active gradually asit traveled down the hole, where tem-perature rises steadily with increasingdepth. The delayed activity would pro-vide more time for the sand mixture tospread through the oil-bearing strata,and the tolerance of heat and salt wouldenable the enzyme to function longerfor breaking down the guar. Preliminarylaboratory tests of this prospect, byRobert M. Kelly of North Carolina StateUniversity, have been encouraging.

If the only sources of extremozymeswere large-scale cultures of extremo-philes, widespread industrial applica-tions of these proteins would be imprac-

tical. Scientists rarely find large quanti-ties of a single species of microbe in na-ture. A desired organism must be puri-fied, usually by isolating single cells, andthen grown in laboratory culture. Fororganisms with extreme lifestyles, isola-tion and large-scale production canprove both difficult and expensive.

Harvesting Extremozymes

Fortunately, extremozymes can be pro-duced through recombinant DNAtechnology without massive culturing ofthe source extremophiles. Genes, whichconsist of DNA, specify the composi-tion of the enzymes and other proteinsmade by cells; these proteins carry outmost cellular activities. As long as mi-crobial prospectors can obtain samplegenes from extremophiles in nature orfrom small laboratory cultures, they cangenerally clone those genes and use themto make the corresponding proteins.That is, by using the recombinant DNAtechnologies, they can insert the genesinto ordinary, or domesticated, mi-crobes, which will often use the genesto produce unlimited, pure supplies ofthe enzymes.

Two approaches have been exploitedto identify potentially valuable extrem-ozymes. The more traditional route re-quires scientists to grow at least smallcultures of an extremophile obtainedfrom an interesting environment. If thescientists are looking for, say, protein-

degrading enzymes, they test to seewhether extracts of the cultured cellsbreak down selected proteins. If suchactivity is detected, the researchers turnto standard biochemical methods to iso-late the enzymes responsible for the ac-tivity and to isolate the genes encodingthe enzymes. They then must hope thatthe genes can be induced to give rise totheir corresponding proteins in a do-mesticated host.

In the other approach, investigatorsbypass the need to grow any cultures ofextremophiles. They isolate the DNAfrom all living things in a sample of wa-ter, soil or other material from an ex-treme environment. Then, using recom-binant DNA technology once again,they deliver random stretches of DNAinto a domesticated hostideally oneinsert per host cellwithout knowingthe identities of the genes in those frag-ments. Finally, they screen the coloniesthat grow out, looking for evidence ofactivity by novel enzymes. If they findsuch evidence, they know that an in-serted gene is responsible and that it willwork in the domesticated host. Thismethod thus avoids many bottlenecksin the traditional process. It turns uponly enzymes that can be manufacturedreadily in tried-and-true hosts. And in-vestigators can mine the genes for theenzymes from mixed populations ofmicrobes without needing to cultureextremophiles that might have troublegrowing outside their native milieu.

Extremophiles86 Scientific American April 1997

Archaea Makes Three

In the summer of 1996 a large collaboration ofscientists deciphered the full sequence of units,or nucleotides, in every gene of Methanococcusjannaschiia methane-producing extremophilethat thrives at temperatures near 85 degrees Cel-sius. The results strikingly confirmed the onceridiculed proposal that life consists of three majorevolutionary lineages, not the two that have beenroutinely described in textbooks.

The recognized lineages were the bacteria (withtheir simple cells that lack a true nucleus) and theeukarya (plants, humans and other animals hav-ing cells that contain a nucleus). By comparingmolecules known as ribosomal RNA in many dif-ferent organisms, Carl R. Woese and his collabora-tors at the University of Illinoishad concluded in 1977 that agroup of microbes once classifiedas bacteria and called archaebac-teria belonged, in fact, to a sepa-rate lineage: the archaea. M. jan-

naschii is the first of the archaeans to have had itsgenes sequenced in full.

The sequencing made it possible to compare M.jannaschiis total complement of genes with themany genes that have so far been sequenced inother organisms. Forty-four percent of M. jan-naschiis genes resemble those in bacteria or eu-karya, or both. And consistent with Woesesscheme, fully 56 percent are completely differentfrom any genes yet described.

That M. jannaschii has characteristics of bacteriaand eukarya but also has marked differences sug-gests that archaea and the other two lineageshave a common distant ancestor. Partly becausemany archaea and some bacteria are adapted tothe conditions widely believed to have existed onthe early earthespecially high heat and little or

no oxygena majority of investi-gators suspect that those twogroups appeared first, divergingfrom a common ancestor rela-tively soon after life began. Later,the eukarya split off from the ar-

ALVIN (top), a scientific submarine, reaches out an arm(middle) to snag material around a deep-sea vent. Meth-anococcus jannaschii, a spherical cell with many flagella,was among its finds in 1982. The diagram on the oppositepage depicts the three major evolutionary lineages of life.

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Although the microbes of the worldare incredibly diverse, scientists rarelyfind in them the perfect enzyme for agiven task. Therefore, microbiologistsat the cutting edge of industrial enzymetechnology have begun to modify ex-tremozymes, tailoring them to meetspecific demands. For instance, afterfinding an extremozyme that degradesproteins fairly efficiently at high tem-peratures, investigators might alter theenzyme so that it functions across abroader range of acidity and salinity.

Biologists today generally achieve suchmodifications in either of two ways.Practitioners of the rational design ap-proach first discern the structural basisof the property of interest. Next, theyalter an enzymes gene to guaranteethat the resulting catalytic protein will

gain that property. Devotees of the oth-er approach, known as directed evolu-tion, make more or less random varia-tions in the gene encoding a selected en-zyme and, from those genes, generatethousands of different versions of theenzyme. Then they screen the collectionto see whether any of the variations hasgained the hoped-for feature. This laststrategy is also said to be Edisonian, be-cause when Thomas Edison sought amaterial to serve as a filament for thelightbulb, he tried everything available,from bamboo splints to silk threads, andchose the one that worked best.

So far most extremozymes in com-mercial use are little altered from theiroriginal state. But rational design andEdisonian approaches promise to en-hance extremozymes. They may also

help to convert enzymes from ordinarymicrobes into artificial extremozymes.

Discovery of extremophiles opens newopportunities for the development of en-zymes having extraordinary catalytic ca-pabilities. Yet for any new enzyme togain commercial acceptance, its makerswill have to keep down the costs of pro-duction, for example, by ensuring thatthe domesticated microbes used as theextremozyme-producing factory willreliably generate large quantities of theprotein. The difficulties of perfectingmanufacturing techniques, and the re-luctance of industries to change systemsthat already work reasonably well, couldslow the entry of new extremozymes intocommerce. It seems inevitable, howev-er, that their many advantages will even-tually prove irresistible.

Extremophiles Scientific American April 1997 87

GRAM-POSITIVEBACTERIA

PURPLE BACTERIA

CYANOBACTERIA

FLAVOBACTERIA

THERMOTOGA

AQUIFEX

PYRODICTIUM

THERMOPROTEUS

THERMO-COCCUS

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METHANOBACTERIUM HALOBACTERIUM

THERMOPLASMA

METHANOPYRUS

ENTAMOEBAESLIME MOLDS ANIMALS

FUNGI

PLANTS

CILIATES

FLAGELLATES

MICROSPORIDIADIPLOMONADS

UNIVERSAL ANCESTOR

BACTERIA ARCHAEA EUKARYA

chaea. Further support for this scenario can be seen in the evolu-tionary tree itself: hyperthermophilic, oxygen-sensitive organ-isms, such as Methanopyrus (archaea) and Aquifex (bacteria),branch off close to the root.

Scientists are eager to learn the nature of the genes that areunique to archaea. Genes are the blueprints from which en-

zymes and other proteins important to cell structure and func-tion are made. Many of the unique archaeal genes undoubtedlyencode novel proteins that may provide insights into how an-cient cells survived. And certain of these unusual proteins canprobably be enlisted for developing innovative medicines or toperform new tricks in industry. M.T.M. and B.L.M.

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Further Reading

Enzymes Isolated from Microorganisms That Grow in Ex-treme Environments. M.W.W. Adams and R. M. Kelly in Chem-ical and Engineering News, Vol. 73, No. 51, pages 3242; Decem-ber 18, 1995.

Extremophiles. Special issue of Federation of European Microbi-ological Societies (FEMS) Microbiology Reviews, Vol. 18, Nos.23; May 1996.

Hyperthermophiles in the History of Life. K. O. Stetter inEvolution of Hydrothermal Ecosystems on Earth (and Mars?).Edited by Gregory R. Bock and Jamie A. Goode. John Wiley &Sons, 1996.

Brock Biology of Microorganisms. Eighth edition. Michael T.Madigan, John M. Martinko and Jack Parker. Prentice Hall, 1997.

The Authors

MICHAEL T. MADIGAN and BARRY L. MARRS share a par-ticular interest in photosynthetic bacteria. Madigan received hisPh.D. in bacteriology in 1976 under Thomas D. Brock at the Uni-versity of WisconsinMadison. He is now professor of microbiolo-gy at Southern Illinois University at Carbondale. Madigans studiesfocus on the biodiversity and metabolic characteristics of photo-synthetic bacteria, especially in extreme environments. Marrs re-ceived his Ph.D. in biology from Case Western Reserve Universityin 1968. He then spent several years in academics and industry, re-cently as the founding chief executive officer of Recombinant Bio-catalysis, which is commercializing enzymes from extremophiles. Heis currently founder and head of a new company, PhotosyntheticHarvest, which plans to make use of the chemicals in green plants.

SA

Copyright 1997 Scientific American, Inc.