It’S PROBABLY NOt a good idea to take too personal an interest in your microbes. LouisPasteur, t Frenc and bacteriologist, became so preoccupied  ook to peering critically at every dis tpresumably did not ations to dinner.

    In fact, t in trying to eria, for t conceive. If you are in good  about one trillion bacteria grazing on your fles a imeter of skin. to dineoff ten billion or so flakes of skin you sasty oils and fortifyingminerals t seep out from every pore and fissure. You are for timate food court,ant mobility they giveyou B.O.

    And t teria t in your skin. trillions more tucked a and nasal passages, clinging to your eetive system alone is to more trillion microbes, of at least four ypes. Some deal arctack oteria. A surprising number, like tous intestinal spiroces, ectable function at all. t seem to like tobe s of about 10 quadrillion cells, but about 100quadrillion bacterial cells. t, a big part of us. From teria’s point ofvie of them.

    Because ilize antibiotics anddisinfectants, it is easy to convince ourselves t o tence. Don’t you believe it. Bacteria may not build cities or eresting social lives,but t, and  onlybecause to be.

    Bacteria, never forget, got along for billions of years  us. e couldn’t survive a day tes and make t tmunc. ter and keep our soils productive. Bacteriasyntamins in our gut, convert t into useful sugars andpolysacco  slip do.

    e depend totally on bacteria to pluck nitrogen from t it into usefulnucleotides and amino acids for us. It is a prodigious and gratifying feat. As Margulis andSagan note, to do trially (as urers must terials to 500 degrees centigrade and squeeze to timesnormal pressures. Bacteria do it all time  fuss, and t trogen tinue toprovide us o keep tmospable. Microbes, including teria, supply ter part of t’s breathable oxygen.

    Algae and otiny organisms bubbling a about 150 billion kilos oftuff every year.

    And tic among tionin less ten minutes; Clostridium perfringens, ttle organism t causesgangrene, can reproduce in nine minutes. At suce, a single bacterium could ticallyproduce more offspring in tons in tesupply of nutrients, a single bacterial cell can generate 280,000 billion individuals in a singleday,” according to t and Nobel laureate Cian de Duve. In t about manage a single division.

    About once every million divisions, tant. Usually tant—c just occasionally terium isendoal advantage, sucy to elude or stack ofantibiotics. ity to evolve rapidly goes anotage. Bacteriasion. Any bacterium can take pieces of genetic coding from any other.

    Essentially, as Margulis and Sagan put it, all bacteria sive c occurs in one area of terial universe can spread to any ot’srato an insect to get tic coding to sprout  means t from a genetic point of vieeria iny, dispersed, but invincible.

    t anyt givettle moisture—as ed from not als in . Scientists in Australia found microbes knoivorans t livedin—indeed, could not live —concentrations of sulfuric acid strong enougo dissolvemetal. A species called Micrococcus radiope tanksof nuclear reactors, gorging itself on plutonium and eriabreak do at all.

    ts and lakes of caustic soda, deep insiderocks, at ttom of ter in tarctica, and seven miles doimes greater t t to being squasyjumbo jets. Some of to be practically indestructible. Deinococcus radiodurans is,according to t , “almost immune to radioactivity.” Blast its DNA ion,and tely reform “like ttling limbs of an undead creature from ahorror movie.”

    Per extraordinary survival yet found  of a Streptococcus bacteriumt  ood on two years.

    In s, ts in  prepared to live. “t s so  t tually startto melt, teria even toria Bennett told me.

    In tists at ty of Cin and Frank Greer,announced t ted from oil rains of bacteria t dept. tion ally preposterous—to live on at t—and for fifty years it  taminated  t ofmicrobes living deep  all to do  rocks or, ratuff t’s in rocks—iron, sulfur, manganese,and so on. And too—iron, c, even uranium. Sucrumental in concentrating gold, copper, and otals, andpossibly deposits of oil and natural gas. It ed t tireless nibblingscreated t.

    Some scientists no trillion tons of bacteria livingbeneat in otropems—SLiME for s. timated t if you took all teria out ofterior and dumped it on t  to a dept. If timates are correct, top of it.

    At deptremely sluggis of tury, some no more than perhaps once in five hundred years.

    As t  it: “to long life, it seems, is not to do too mucougeria are prepared to s doems and  for bettertimes. In 1997 scientists successfully activated some ant  foreigrondback to life after being released from a 118-year-old can of meat and a 166-year-old bottle ofbeer. In 1996, scientists at to eriafrozen in Siberian permafrost for t ty so faris one made by Russell Vreeland and colleagues at est Cer University in Pennsylvaniain 2000, ated 250-million-year-old bacteria calledBacillus permians t rapped in salt deposits t underground inCarlsbad, Neinents.

    t met andable dubiousness. Many biocs maintained tover sucs self from time to time. erium did stir occasionallyternal source of energy t could ed so long. tful scientists suggested t taminated, if not during itsretrieval till buried. In 2001, a team from tel Aviv University argued tB. permians  identical to a strain of modern bacteria, Bacillus marismortui, foundin ts genetic sequences differed, and tly.

    “Are o believe,” te, “t in 250 million years B. permiansed t of genetic differences t could be ac 3–7days in tory?” In reply, Vreeland suggested t “bacteria evolve faster in the wild.”

    Maybe.

    It is a remarkable fact t o t scextbooks divided to just tegories—plant and animal. Microorganisms ured.

    Amoebas and similar single-celled organisms reated as proto-animals and algae asproto-plants. Bacteria s, too, even t belong te nineteentury turalistErnst ed t bacteria deserved to be placed in a separate kingdom,  begin to catcs until te t my trusty American age desk dictionaryfrom 1969 doesn’t recognize term.)Many organisms in traditional division.

    Fungi, t includes muss, and puffballs, reated as botanical objects, t almost not tc world.

    Structurally t tin,a material t gives tinctive texture. tance is used to make ts and t isn’t nearly so tasty in a stag beetle as ina Portobello muss, fungi don’t posynt green. Instead tly on t anyt te ter betoes—t  tlike quality t t.

    Even less comfortably susceptible to categorization es but more commonly knoo do y. An appellation t sounded a little more dynamic—“ambulant self-activating protoplasm,” say—and less like tuff you find  certainly raordinary entities amore immediate stention take,among t interesting organisms in nature. imes are good, t as one-celled individuals, muc ougo acentral gat miraculously, a slug. t a ty and it doesn’t go terribly far—usually just from ttom of a pile of leaf litter to top,  for millions of years tiest trick in the universe.

    And it doesn’t stop tself up to a more favorable locale, transforms itself yet again, taking on t. By some curious orderlyprocess tiny marco make a stalk atopof ing body are millions ofspores t, at te moment, are released to to blo can start the process again.

    For years slime molds ozoa by zoologists and as fungi by mycologists,t people could see t really belong anyestingarrived, people in lab coats o find t slime molds inctive andpeculiar t t directly related to anyture, and sometimes not evento eacher.

    In 1969, in an attempt to bring some order to tion, anecologist from Cornell University named R. taker unveiled in to divide life into five principal brancae, Fungi, Protista, and Monera. Protista, ion of an earlierterm, Protoctista, ury earlier by a Scottis namedJo to describe any organisms t  nor animal.

    ttaker’s ne, Protista remained ill defined.

    Some taxonomists reserved it for large unicellular organisms—tes—but otreated it as tting into it anyt didn’t fitany you consulted) slime molds, amoebas,and even sea contained as many as 200,000different species of organism all told. t’s a lot of odd socks.

    Ironically, just as taker’s five-kingdom classification o find its o textbooks, a retiring academic at ty of Illinois   o do so—lystudying genetic sequences in bacteria. In takingprocess. ork on a single bacterium could easily consume a year. At t time, according tooese, only about 500 species of bacteria  ten times t, t is stillfar s of tedorganisms whe annals of biology.

    It isn’t simple indifference t keeps total loeria can be exasperatingly difficultto isolate and study. Only about 1 percent ure. Considering able ture, it is an odd fact t t to ri dis  liet to bloom. Any bacterium t tion exceptional, and yet t exclusively, tudied bymicrobiologists. It  animals from visiting zoos.”

    Genes, o approac tal divisions in ted. A lot of little organisms t looked like bacteria and beeria ually sometoget eria a long time ago. oese called teria, later sened toarchaea.

    It  ttributes t distinguiseria are not t t a biologist. tly differences in tidoglycan. But in practice t from bacteria ted division of life, so fundamentalt it stood above t tree of Life, as it isratially known.

    In 1976, artled t least ttle bit of it t tention—byredraree of life to incorporate not five main divisions, but ty-tegories—Bacteria, Arcimesspelled Eucarya)—which he called domains.

    oese’s ne take torm. Some dismissed too ed to ignored to Frances As, “felt bitterly disappointed.” But slocs. Botanists and zoologists s virtues.

    It’s not o see edto a feermost brancounicellular beings.

    “t up to classify in terms of gross morpies anddifferences,” oese told an intervieerms of molecularsequence is a bit o s see a difference like it. And so ted raditional five-kingdom division—an arrangement t oese called “not very useful” in s and “positively misleading” muc of time. “Biology, like p,” oese e, “o a level erest and teractions often cannot be perceived t observation.”

    In 1998 t and ancient  Ernst Mayr ( time of my ing is nearing one ill going strong) stirredt furt t two prime divisions of life—“empires”

    ional Academy of Sciences,Mayr said t oese’s findings eresting but ultimately misguided, noting t“oese  trained as a biologist and quite naturally does not ensivefamiliarity ion,”  can come to saying of anot  kno.

    ticisms are too teco need extensive airing ic sexuality, ion, and controversial interpretationsof terium trop else—butessentially  oese’s arrangement unbalances tree of life. terialrealm, Mayr notes, consists of no more to be found—“but .” By contrast, tic realm—t is, ted organisms ed cells, like us—numbers already in terial organisms in a single category,Prokaryota,  anothe living world.”

    tinction beteriaand gram-positive bacteria clearly ter of moment for most of us, but it is eac from its neigs. Ifoese’s ne teac is t life really is various and t most oft variety is small, unicellular, and unfamiliar. It is a natural o tion as a long cs, of a never-ending advance toy—in a oter ourselves. Most of ty inevolution  flukes—an interesting side brancy-ts, animals, and fungi—are largeenougo be seen by tain species t are microscopic.

    Indeed, according to oese, if you totaled up all t—every livingts included—microbes  for at least 80 percent of all to t ime.

    So  some point in your life, do microbes so often  to us?  possible satisfaction could to a microbe in , after all, is oprovide long-term ality.

    to begin  is  most microorganisms are neutral or evenbeneficial to  rampantly infectious organism on Earterium called olbac   all—or, come to t, any otebrates—but if you are a s fly, it can make you  one microbe in a to National Geograp some of t t is quite enougly benign, microbes are still tern ence.

    Making a  uns for toms of an illnessoften o spread ting, sneezing, and diarr metting out of one  and into position for anot effective strategy of all is toenlist ty. Infectious organisms love mosquitoes because to’s sting delivers tly to a bloodstream raigo im’s defense mec is, and a ed but often rapacious maladies—begin o bite. It is afortunate fluke for us t , isn’t among t least not yet. Any o sucks up on its travels is dissolved by to’s oabolism.  tates its rouble.

    It is a mistake, o consider tter too carefully from tion of logicbecause microorganisms clearly are not calculating entities. t care oyou any more t distress you cause . time your continuing o a pat kills you too e you before t t sometimes ory,Jared Diamond notes, is full of diseases t “once caused terrifying epidemics and teriously as tes t but mercifully transientEnglising sickness, ens of t, before burning itself out. too muc a good tiousorganism.

    A great deal of sickness arises not because of o you but rying to do to ts quest to rid tem sometimes destroys cells or damages critical tissues, so often  t your oting sick is a sensible response to infection. Sick people retire to t to ty. Resting also frees more of toattend to tion.

    Because t tential to  you, your body s of different varieties of defensive en million types in all, eaco identify and destroy a particular sort of invader. It to maintain ten million separate standing armies, so eacy of s on active duty. ious agent—igen—invades,relevant scouts identify ttacker and put out a call for reinforcements of t type.

    uring to feel c ofrecovery begins o action.

    e cells are merciless and  patoavoid extinction, attackers al strategies. Eitrike quicklyand move on to a neious illnesses like flu, or t te cells fail to spot t iced in to action.

    One of ts of infection is t microbes t normally do no  allsometimes get into ts of the words of Dr.

    Bryan Marsious diseases specialist at Dartmoutcer inLebanon, Nes  are normally benign in t get into ots of tream, for instance—and cause terrible havoc.”

    t, most out-of-control bacterial disorder of t is a disease callednecrotizing fasciitis in ially eat tim from t, devouringinternal tissue and leaving beients often come in ively mild complaints—a skin rasypically—but ticallydeteriorate.  is often found t they are simply being consumed.

    treatment is ting out every bit ofinfected area. Seventy percent of victims die; many of t are left terribly disfigured. tion is a mundane family of bacteria called Group A Streptococcus, . Very occasionally, for reasons unknoeria get t and into t devastating ely resistant to antibiotics. About ated States, and no one can say t it  get worse.

    Precisely tis. At least 10 percent of young adults, andper of teenagers, carry terium, but it lives quite. Just occasionally—in about one young person in a  gets into tream and makes t cases,deat and dead by evening,” says Marsh.

    e  so profligate  tibiotics. Remarkably, by one estimate some 70 percent of tibiotics used in to farm animals, often routinely in stockfeed, simply to promote gro infection. Sucions givebacteria every opportunity to evolve a resistance to t is an opportunity t tically seized.

    In 1952, penicillin ive against all strains of staperia, to sucent t by te, felt confidentenougo declare: “time o close tious diseases. e  infection in ted States.” Even as  of trains y to penicillin. Soon one oftrains, called Metant Stapo sals. Only one type of antibiotic, vancomycin, remained effective against it, but in 1997a al in tokyo reported train t could resist even t. it o six otals. All over, toals alone, some fourteen tions ted, given a cibiotics t people ake every day for tidepressants tpeople ake every day forever, drug companies not surprisingly opt for tter.

    Altibiotics oug, tical industry given us an entirely neibiotic since the 1970s.

    Our carelessness is all t many ots maybe bacterial in origin. torin Pertern Australia, found t many stomac stomacerium called er pylori. Even tested,tion  more ted. America’s National Institutes of ance, didn’t officially endorse til 1994. “  old a reporter from Forbes in 1999.

    Since t terial component inall kinds of ot disease, astis, multiple sclerosis, several typesof mental disorders, many cancers, even, it ed (inScience no less), obesity.

    t be far off ive antibiotic and got one to call on.

    It may come as a slig to kno bacteria can t sick. times infected by bacteriopype of virus. A virus is a strangeand unlovely entity—“a piece of nucleic acid surrounded by bad nee Peter Medaeria, viruses aren’ttion t and  introduce to a suitable and t into busyness—into life. About five types of virus are kno us o t are most invidious to he source of AIDS.

    Viruses prosper by ic material of a living cell and using it to producemore virus. tical manner, t out in searcoinvade. Not being living organisms to be very simple. Many,including en genes or feeria require severaltiny, mucoo small to be seen ional microscope.

    It  until 1943 and tion of tron microscope t science got its first lookat t tietury alone killed anestimated 300 million people.

    ty to burst upon tartlingform and to vaniso come dorange sleeping sickness, ims o sleep and not  great difficulty to take food or go to tory, and ionssensibly—tic.

    tted to rest, t once back intodeepest slumber and remain in t state for as long as t. Some  on in t notted in a state of profound apatinct volcanoes,” intor. In ten years tly  a didn’t get mucing attention because in time an even  in ory—s across the world.

    It is sometimes called t Simes t Spanis in eit y-one million people infour years; ss first four mont 80 percent of Americancasualties in t orld ar came not from enemy fire, but from flu. In some units tality rate was as .

    S some mutated into sometims suffered only mild symptoms, but t became gravely ill and often died.

    Some succumbed hers held on for a few days.

    In ted States, t deaton in late August1918, but to all parts of try. Scertainments tle good. Betumn of 1918 and spring of toll in Britain h similar numbers dead in France and Germany.

    No one knooll, as records in ten poor, but it less timates  total as high as 100 million.

    In an attempt to devise a vaccine, medical auties conducted tests on volunteers at amilitary prison on Deer Island in Boston tery of tests. tests o say t. First ts ed ed lung tissue taken from tious aerosols. If till failed to succumb, ts saken from to sitopen-moutim heir faces.

    Out of—someeered, tors cy-tests. None contracted t one. tor, ion for t teers, all of ation, ural immunity.

    Muc tood poorly or not at all. One mystery is  eruptedsuddenly, all over, in places separated by oceans, mountain ranges, and ots. A virus can survive for no more tside a  body, so  appear in Madrid, Bombay, and Phe same week?

    t it ed and spread by people oms or none at all. Even in normal outbreaks, about 10 percent of people  are una because ts. And because tion tend to be t spreaders of the disease.

    t  for tbreak’s ribution, but it still doesn’texplain  managed to lay loing so explosively at moreor less time all over. Even more mysterious is t it ating topeople in t on infants and t in tbreak deaties and ties. Olderpeople may ed from resistance gained from an earlier exposure to train,but  mystery of all is . e still have no idea.

    From time to time certain strains of virus return. A disagreeable Russian virus kno againin t  in time eacime is uncertain. One suggestion is tviruses  unnoticed in populations of rying t a neion of  ty t t Swine Flu epidemicmigs head.

    And if it doesn’t, ot. New and frigime.

    Ebola, Lassa, and Marburg fevers all ended to flare up and die do no onecan say t t quietly mutating aopportunity to burst fortastrop is no t AIDS ed. Researc terRoyal Infirmary in England discovered t a sailor reatablecauses in 1959 in fact  for  for anoty years.

    t ot gone rampant. Lassa fever,  detected until 1969, in est Africa, is extremely virulent and little understood. In 1969, adoctor at a Yale University lab in Ne, . , more alarmingly, a tec exposure, also contracted the disease and died.

    break stopped t  count on sucune alyles invite epidemics. Air travel makes it possible to spread infectious agents across t  inNe medical autiesincreasingly need to be acquainted ty muc exists every. In 1990, a Nigerian living in Co Lassa fever on avisit to  didn’t develop symptoms until urned to ted States.

    al  diagnosis and  anyone taking any specialprecautions in treating   letious diseaseson t. Miraculously, no one else ed. e may not be so lucky next time.

    And on t sobering note, it’s time to return to the visibly living.