Medical Microbiology

174 3 GeneralBacteriology

IntercellularMechanismsofGeneticVariability..........

Althoughbacteriahavenosexualheredityinthestrictsense,theydohave

mechanismsthatallowforintercellularDNAtransfer.Thesemechanisms,

whichinvolveaunilateraltransferofgeneticinformationfromadonor

celltoareceptorcell,aresubsumedunderthetermparasexuality.

Transformation........................................

Transferof“naked”DNA.In 1 928,Griffithdemonstratedthattheabilityto

produceacertaintypeofcapsulecouldbetransferredbetweendifferent

pneumococci.ThenAveryshowedin 1944 thatthetransformingprinciple

atworkwasDNA.Thistransformationprocesshasbeenobservedmainly

inthegeneraStreptococcus,Neisseria,HelicobacterandHaemophilus.

Transduction...........................................

TransferofDNAfromadonortoareceptorwiththehelpoftransportbacte-

riophages(Fig.3. 21 ).

Transduction

a

b

Donor cell Receptor cell Recombination

Fig.3. 21 TransductionofachromosomalDNAsequence(a)andaplasmid(b).

3

Kayser, Medical Microbiology © 2005 Thieme