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*欧阳光明*创编2021.03.07DigestOfThe.Economist.2006(6-7欧阳光明（2021.03.07）
HardtodigestAwealthofgeneticinformationistobefoundinthehumangut
BACTERIA,likepeople,canbedividedintofriendandfoe.Inspiredbyevidencethatthefriendlysortmayhelpwitharangeofailments,manypeopleconsumebacteriaintheformofyogurtsanddietarysupplements.Suchasmatteringofartificialadditions,however,representsbutadropintheocean.Thereareatleast800typesofbacterialivinginthehumangut.AndresearchbyStevenGilloftheInstituteforGenomicResearchinRockville,Maryland,andhiscolleagues,publishedinthisweek'sScience,suggeststhatthecollectivegenomeoftheseorganismsissolargethatitcontains100timesasmanygenesasthehumangenomeitself.DrGillandhisteamwereabletocometothisconclusionbyextractingbacterialDNAfromthefaecesoftwovolunteers.Becauseofthecomplexityofthesamples,theywerenotabletoreconstructtheentiregenomesofeachofthegutbacteria,justtheindividualgenes.Butthatallowedthemtomakeanestimateofnumbers.Whatallthesebacteriaaredoingistrickytoidentify—thebacteriathemselvesaredifficulttocultivate.Sotheresearchersguessedatwhattheymightbeuptoby*欧阳光明*创编2021.03.07
*欧阳光明*创编2021.03.07comparingthegenestheydiscoveredwithpublisheddatabasesofgeneswhosefunctionsarealreadyknown.ThiscomparisonhelpedDrGillidentifyforthefirsttimetheprobableenzymaticprocessesbywhichbacteriahelphumanstodigestthecomplexcarbohydratesinplants.Thebacteriaalsocontainaplentifulsupplyofgenesinvolvedinthesynthesisofchemicalsessentialtohumanlife—includingtwoBvitaminsandcertainessentialaminoacids—althoughtheteammerelyshowedthatthesemetabolicpathwaysexistratherthanprovingthattheyareused.Nevertheless,thepathwaystheyfoundleavehumanslookingmorelikeruminants:animalssuchasgoatsandsheepthatusebacteriatobreakdownotherwiseindigestiblematterintheplantstheyeat.ThebroaderconclusionDrGilldrawsisthatpeoplearesuperorganismswhosemetabolismrepresentsanamalgamationofhumanandmicrobialattributes.Thenotionofasuperorganismhasemergedbefore,asresearchersinotherfieldshavecometoviewhumansashavingadiverseinternalecosystem.This,suggestsome,willbecrucialtothesuccessofpersonalisedmedicine,asdifferentpeoplewillhavedifferentresponsestodrugs,dependingontheirmicrobialflora.Accordingly,thenextstep,saysDrGill,istoseehowmicrobialpopulationsvarybetweenpeopleofdifferentages,backgroundsanddiets.Anotherareaofresearchistheprocessbywhichthesehelpfulbacteriafirstcolonisethedigestivetract.Babiesacquiretheirgutfloraastheypassdownthebirthcanalandtakeagene-filledgulpoftheirmother'svaginalandfaecalflora.Itmightnotbethemostdeliciousoffirstmeals,butitcouldwellbeanimportant*欧阳光明*创编2021.03.07

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