How It Works - UK (2020-05)

Scientists discover massive

bacteria-eating viruses

WordsbyYaseminSaplakoglu

H

ugebacteria-killingviruseslurkin

ecosystemsaroundtheworld,fromhot

springstofreshwaterlakesandrivers.

Now,a groupofresearchershasdiscoveredsome

oftheseso-calledbacteriophagesthataresolarge

andsocomplexthattheyblurthelinebetween

livingandnonliving,accordingtonewfindings.

Bacteriophages,or‘phages’forshort,are

virusesthatspecificallyinfectbacteria.Phages

andothervirusesarenotconsideredliving

organismsbecausetheycan’tcarryoutbiological

processeswithoutthehelp and cellular machinery

ofanotherorganism.

Thatdoesn’tmeantheyareinnocuous:phages

aremajordriversofecosystemchangebecause

theypreyonpopulationsofbacteria,altertheir

metabolism,spreadantibioticresistanceand

carrycompoundsthatcausediseaseinanimals

andhumans,accordingtoscientists from the

UniversityofCalifornia.

Tolearnmoreaboutthesesneakyinvaders,the

scientistssearchedthrougha DNAdatabasethat

theycreatedfromsamplestheyandtheir

colleaguescollectedfromnearly 30 different

environmentsaroundtheworld,rangingfromthe

gutsofpeopleandAlaskanmoosetoa South

Africanbioreactoranda Tibetanhotspring.

FromthatDNAtheydiscovered 351 hugephages

that had genomes four or more times larger than

theaveragegenomeofphages.Amongthosewas

thelargestphagefoundtodatewitha genomeof

735,000basepairs– thepairsofnucleotidesthat

makeuptherungsoftheDNAmolecule’s‘ladder’

structure– ornearly15-timeslargerthanthe

averagephage.Forreference,thehuman genome

containsabout3 billionbasepairs.

Thesephagesare“hybridsbetweenwhatwe

thinkofastraditionalvirusesandtraditional

livingorganisms”suchasbacteriaandarchaea,

saidJillBanfield,a UniversityofCalifornia,

BerkeleyprofessorofEarthandplanetaryscience.

Thishugephages’genomeismuch larger than the

genomesofmanybacteria.

Theresearchersfoundthatmanyofthegenes

codedforproteinsareyetunknowntous.They

foundthatthephageshada numberofgenesthat

arenottypicalofvirusesbutaretypicalof

bacteria.Someofthesegenesarepartofa system

thatbacteriausetofightvirusesandwaslater

adaptedbyhumanstoedit genes – a technique

calledCRISPR-Cas9.

Scientistsdon’tknowforsure,buttheythink

thatoncethesephagesinjecttheirDNAinto

bacteria,thephages’ownCRISPRsystem

strengthenstheCRISPRsystemofthebacteria.

InthatwaythecombinedCRISPRsystemcould

helptotargetotherphages – getting ridof

the competition.

A newlydiscovered

virusis blurringthe

linesbetweenliving

and nonliving

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