万物简史英文版_比尔·布莱森- 第63部分

we　depend　totally　on　bacteria　to　pluck　nitrogen　from　the　air　and　convert　it　into　usefulnucleotides　and　amino　acids　for　us。　it　is　a　prodigious　and　gratifying　feat。　as　margulis　andsagan　note；　to　do　the　same　thing　industrially　（as　when　making　fertilizers）　manufacturers　mustheat　the　source　materials　to　500　degrees　centigrade　and　squeeze　them　to　three　hundred　timesnormal　pressures。　bacteria　do　it　all　the　time　without　fuss；　and　thank　goodness；　for　no　largerorganism　could　survive　without　the　nitrogen　they　pass　on。　above　all；　microbes　continue　toprovide　us　with　the　air　we　breathe　and　to　keep　the　atmosphere　stable。　microbes；　including　themodern　versions　of　cyanobacteria；　supply　the　greater　part　of　the　planet鈥檚　breathable　oxygen。

algae　and　other　tiny　organisms　bubbling　away　in　the　sea　blow　out　about　150　billion　kilos　ofthe　stuff　every　year。

and　they　are　amazingly　prolific。　the　more　frantic　among　them　can　yield　a　new　generationin　less　than　ten　minutes；　clostridium　perfringens；　the　disagreeable　little　organism　that　causesgangrene；　can　reproduce　in　nine　minutes。　at　such　a　rate；　a　single　bacterium　could　theoreticallyproduce　more　offspring　in　two　days　than　there　are　protons　in　the　universe。　鈥済iven　an　adequatesupply　of　nutrients；　a　single　bacterial　cell　can　generate　280；000　billion　individuals　in　a　singleday；鈥潯�according　to　the　belgian　biochemist　and　nobel　laureate　christian　de　duve。　in　the　sameperiod；　a　human　cell　can　just　about　manage　a　single　division。

about　once　every　million　divisions；　they　produce　a　mutant。　usually　this　is　bad　luck　for　themutant鈥攃hange　is　always　risky　for　an　organism鈥攂ut　just　occasionally　the　new　bacterium　isendowed　with　some　accidental　advantage；　such　as　the　ability　to　elude　or　shrug　off　an　attack　ofantibiotics。　with　this　ability　to　evolve　rapidly　goes　another；　even　scarier　advantage。　bacteriashare　information。　any　bacterium　can　take　pieces　of　genetic　coding　from　any　other。

essentially；　as　margulis　and　sagan　put　it；　all　bacteria　swim　in　a　single　gene　pool。　anyadaptive　change　that　occurs　in　one　area　of　the　bacterial　universe　can　spread　to　any　other。　it鈥檚rather　as　if　a　human　could　go　to　an　insect　to　get　the　necessary　genetic　coding　to　sprout　wingsor　walk　on　ceilings。　it　means　that　from　a　genetic　point　of　view　bacteria　have　bee　a　singlesuperorganism鈥攖iny；　dispersed；　but　invincible。

they　will　live　and　thrive　on　almost　anything　you　spill；　dribble；　or　shake　loose。　just　givethem　a　little　moisture鈥攁s　when　you　run　a　damp　cloth　over　a　counter鈥攁nd　they　will　bloom　asif　created　from　nothing。　they　will　eat　wood；　the　glue　in　wallpaper；　the　metals　in　hardenedpaint。　scientists　in　australia　found　microbes　known　as　thiobacillus　concretivorans　that　livedin鈥攊ndeed；　could　not　live　without鈥攃oncentrations　of　sulfuric　acid　strong　enough　to　dissolvemetal。　a　species　called　micrococcus　radiophilus　was　found　living　happily　in　the　waste　tanksof　nuclear　reactors；　gorging　itself　on　plutonium　and　whatever　else　was　there。　some　bacteriabreak　down　chemical　materials　from　which；　as　far　as　we　can　tell；　they　gain　no　benefit　at　all。

they　have　been　found　living　in　boiling　mud　pots　and　lakes　of　caustic　soda；　deep　insiderocks；　at　the　bottom　of　the　sea；　in　hidden　pools　of　icy　water　in　the　mcmurdo　dry　valleys　ofantarctica；　and　seven　miles　down　in　the　pacific　ocean　where　pressures　are　more　than　athousand　times　greater　than　at　the　surface；　or　equivalent　to　being　squashed　beneath　fiftyjumbo　jets。　some　of　them　seem　to　be　practically　indestructible。　deinococcus　radiodurans　is；according　to　theeconomist　；　鈥渁lmost　immune　to　radioactivity。鈥潯�blast　its　dna　with　radiation；and　the　pieces　immediately　reform　鈥渓ike　the　scuttling　limbs　of　an　undead　creature　from　ahorror　movie。鈥�

perhaps　the　most　extraordinary　survival　yet　found　was　that　of　a　streptococcus　bacteriumthat　was　recovered　from　the　sealed　lens　of　a　camera　that　had　stood　on　the　moon　for　two　years。

in　short；　there　are　few　environments　in　which　bacteria　aren鈥檛　prepared　to　live。　鈥渢hey　arefinding　now　that　when　they　push　probes　into　ocean　vents　so　hot　that　the　probes　actually　startto　melt；　there　are　bacteria　even　there；鈥潯�victoria　bennett　told　me。

in　the　1920s　two　scientists　at　the　university　of　chicago；　edson　bastin　and　frank　greer；announced　that　they　had　isolated　from　oil　wells　strains　of　bacteria　that　had　been　living　atdepths　of　two　thousand　feet。　the　notion　was　dismissed　as　fundamentally　preposterous鈥攖herewas　nothing　to　live　on　at　two　thousand　feet鈥攁nd　for　fifty　years　it　was　assumed　that　theirsamples　had　been　contaminated　with　surface　microbes。　we　now　know　that　there　are　a　lot　ofmicrobes　living　deep　within　the　earth；　many　of　which　have　nothing　at　all　to　do　with　theorganic　world。　they　eat　rocks　or；　rather；　the　stuff　that鈥檚　in　rocks鈥攊ron；　sulfur；　manganese；and　so　on。　and　they　breathe　odd　things　too鈥攊ron；　chromium；　cobalt；　even　uranium。　suchprocesses　may　be　instrumental　in　concentrating　gold；　copper；　and　other　precious　metals；　andpossibly　deposits　of　oil　and　natural　gas。　it　has　even　been　suggested　that　their　tireless　nibblingscreated　the　earth鈥檚　crust。

some　scientists　now　think　that　there　could　be　as　much　as　100　trillion　tons　of　bacteria　livingbeneath　our　feet　in　what　are　known　as　subsurface　lithoautotrophic　microbial　ecosystems鈥攕lime　for　short。　thomas　gold　of　cornell　has　estimated　that　if　you　took　all　the　bacteria　out　ofthe　earth鈥檚　interior　and　dumped　it　on　the　surface；　it　would　cover　the　planet　to　a　depth　of　fivefeet。　if　the　estimates　are　correct；　there　could　be　more　life　under　the　earth　than　on　top　of　it。

at　depth　microbes　shrink　in　size　and　bee　extremely　sluggish。　the　liveliest　of　them　maydivide　no　more　than　once　a　century；　some　no　more　than　perhaps　once　in　five　hundred　years。

as　the　economist　has　put　it：　鈥渢he　key　to　long　life；　it　seems；　is　not　to　do　too　much。鈥潯�whenthings　are　really　tough；　bacteria　are　prepared　to　shut　down　all　systems　and　wait　for　bettertimes。　in　1997　scientists　successfully　activated　some　anthrax　spores　that　had　lain　dormant　foreighty　years　in　a　museum　display　in　trondheim；　norway。　other　microorganisms　have　leaptback　to　life　after　being　released　from　a　118…year…old　can　of　meat　and　a　166…year…old　bottle　ofbeer。　in　1996；　scientists　at　the　russian　academy　of　science　claimed　to　have　revived　bacteriafrozen　in　siberian　permafrost　for　three　million　years。　but　the　record　claim　for　durability　so　faris　one　made　by　russell　vreeland　and　colleagues　at　west　chester　university　in　pennsylvaniain　2000；　when　they　announced　that　they　had　resuscitated　250…million…year…old　bacteria　calledbacillus　permians　that　had　been　trapped　in　salt　deposits　two　thousand　feet　underground　incarlsbad；　new　mexico。　if　so；　this　microbe　is　older　than　the　continents。

the　report　met　with　some　understandable　dubiousness。　many　biochemists　maintained　thatover　such　a　span　the　microbe鈥檚　ponents　would　have　bee　uselessly　degraded　unless　thebacterium　roused　itself　from　time　to　time。　however；　if　the　bacterium　did　stir　occasionallythere　was　no　plausible　internal　source　of　energy　that　could　have　lasted　so　long。　the　moredoubtful　scientists　suggested　that　the　sample　may　have　been　contaminated；　if　not　during　itsretrieval　then　perhaps　while　still　buried。　in　2001；　a　team　from　tel　aviv　university　argued　thatb。　permians　were　almost　identical　to　a　strain　of　modern　bacteria；　bacillus　marismortui；　foundin　the　dead　sea。　only　two　of　its　genetic　sequences　differed；　and　then　only　slightly。

鈥渁re　we　to　believe；鈥潯�the　israeli　researchers　wrote；　鈥渢hat　in　250　million　years　b。　permianshas　accumulated　the　same　amount　of　genetic　differences　that　could　be　achieved　in　just　3鈥�7days　in　the　laboratory？鈥潯�in　reply；　vreeland　suggested　that　鈥渂acteria　evolve　faster　in　the　labthan　they　do　in　the　wild。鈥�

maybe。

it　is　a　remarkable　fact　that　well　into　the　space　age；　most　school　textbooks　divided　the　worldof　the　living　into　just　two　categories鈥攑lant　and　animal。　microorganisms　hardly　featured。

amoebas　and　similar　single…celled　organisms　were　treated　as　proto…animals　and　algae　asproto…plants。　bacteria　were　usually　lumped　in　with　plants；　too；　even　though　everyone　knewthey　didn鈥檛　belong　there。　as　far　back　as　the　late　nineteenth　century　the　german　naturalisternst　haeckel　had　suggested　that　bacteria　deserved　to　be　placed　in　a　separate　kingdom；　whichhe　called　monera；　but　the　idea　didn鈥檛　begin　to　catch　on　among　biologists　until　the　1960s　andthen　only　among　some　of　them。　（i　note　that　my　trusty　american　heritage　desk　dictionaryfrom　1969　doesn鈥檛　recognize　the　term。）many　organisms　in　the　visible　world　were　also　poorly　served　by　the　traditional　division。

fungi；　the　group　that　includes　mushrooms；　molds；　mildews；　yeasts；　and　puffballs；　were　nearlyalways　treated　as　botanical　objects；　though　in　fact　almost　nothing　about　them鈥攈ow　theyreproduce　and　respire；　how　they　build　themselves鈥攎atches　anything　in　the　plant　world。

structurally　they　have　more　in　mon　with　animals　in　that　they　build　their　cells　from　chitin；a　material　that　gives　them　their　distinctive　texture。　the　same　substance　is　used　to　make　theshells　of　insects　and　the　claws　of　mammals；　though　it　isn鈥檛　nearly　so　tasty　in　a　stag　beetle　as　ina　portobello　mushroom。　above　all；　unlike　all　plants；　fungi　don鈥檛　photosynthesize；　so　theyhave　no　chlorophyll　and　thus　are　not　green。　instead　they　grow　directly　on　their　food　source；which　can　be　almost　anything。　fungi　will　eat　the　sulfur　off　a　concrete　wall　or　the　decayingmatter　between　your　toes鈥攖wo　things　no　plant　will　do。　almost　the　only　plantlike　quality　theyhave　is　that　they　root。

even　less　fortably　susceptible　to　categorization　was　the　peculiar　group　of　organismsformally　called　myxomycetes　but　more　monly　known　as　slime　molds。　the　name　no　doubthas　much　to　do　with　their　obscurity。　an　appellation　that　sounded　a　little　more　dynamic鈥斺�渁mbulant　self…activating　protoplasm；鈥潯�say鈥攁nd　less　like　the　stuff　you　find　when　you　reachdeep　into　a　clogged　drain　would　almost　certainly　have　earned　these　extraordinary　entities　amore　immediate　share　of　the　attention　they　deserve；　for　slime　molds　are；　make　no　mistake；among　the　most　interesting　organisms　in　nature。　when　times　are　good；　they　exist　as　one…celled　individuals；　much　like　amoebas。　but　when　conditions　grow　tough；　they　crawl　to　acentral　gather