Horizontal gene transfer Horizontal gene transfer is the lateral transfer of genetic material between cellular organisms. It happens frequently in prokaryotes, and less frequently in eukaryotes. In bacteria, horizontal gene transfer can occur through transformation (uptake of free floating DNA in the environment), transduction (virus mediated DNA uptake), or conjugation (transfer of DNA between pili structures of two adjacent bacteria). Recent studies have also uncovered other mechanisms, such as membrane vesicle transmission or gene transfer agents. Biofilms promote horizontal gene transfer in a variety of ways.thumb|396x396px|Transmission electron micrograph showing bacteria Escherichia coli that form extensive biofilms using a network of conjugative F-pili. Source: Jonasz PatkowskiBacterial conjugation has been shown to accelerate biofilm formation in difficult environment due to the robust connections established by the conjugative pili. These connections can often foster cross-species transfer events due to the diverse heterogeneity of many biofilms. Additionally, biofilms are structurally confined by a polysaccharide matrix, providing the close spatial requirements for conjugation. Transformation is also frequently observed in biofilms. Bacterial autolysis is a key mechanism in biofilm structural regulation, providing an abundant source of competent DNA primed for transformative uptake. In some instances, inter-biofilm quorum sensing can enhance the competence of free floating eDNA, further promoting transformation. Stx gene transfer through bacteriophage carriers has been witnessed within biofilms, which suggests that biofilms are also a suitable environment for transduction. Membrane vesicles HGT occurs when released membrane vesicles (containing genetic information) fuse with a recipient bacteria, and release genetic material into the bacteria's cytoplasm. Recent research has revealed that membrane vesicle HGT can promote single-strain biofilm formation, yet the role membrane vesicle HGT plays in the formation of multistrain biofilms is still unknown. GTAs, or gene transfer agents, are phage-like particles produced by the host bacteria and contain random DNA fragments from the host bacteria genome. HGT within biofilms can confer antibiotic resistance or increased pathogenicity across the biofilms' population, promoting biofilm homeostasis.
horiZonTal GeNE traNsfer HOriZontal GeNE transfer is thE lateral TransfeR of gENetic matEriAl betweEn cellulAr ORgANISms. It happeNS fRequenTly iN PRokarYotes, aND LESs fREQueNTly in eUkarYotEs. in bacteria, HorizonTaL gene TRaNsfer can occUr throuGH transfOrMaTion (UPtake of fRee FlOatInG dna in the EnVirOnmeNT), tRaNsdUctioN (vIrUs mediated dnA UPtakE), OR conjUGaTion (TraNsfer oF dNa beTWEEN piLi stRucTurEs of twO AdJAcent BaCteria). ReceNt stuDieS hAVe aLSo UnCoverEd OtheR mechaNisms, SUCh aS memBranE VeSICLe TRansMIsSion OR gEnE transfEr agENts. biofiLMs prOmOtE horIzonTal gEne tRanSfer iN a varietY OF WAyS.Thumb|396x396px|tRansMIsSion ElEcTRoN micRograph sHowiNG bactERia escheRIcHIa coli tHaT FORm EXTensIvE BiofIlMs uSiNG A NeTwORK of ConjugATive F-PIli. source: jOnasZ paTkowskIbActerIAl CoNjugatIon HaS beeN sHown to acCElerAte bIoFilM foRmAtion in diffiCUlt EnviroNMENT due TO the roBuSt conNectionS EstablIsheD bY the cOnjUgAtIVe pIli. THese conNEctIonS CaN ofTeN fOstEr cROSs-speciEs TRansfer EvEntS dUe TO thE dIverSE HEtErogeneity Of many BiOfilms. ADditiOnalLY, BiOfiLMs arE strUCturaLlY CoNfIned by A pOlYsAcchAride mATRiX, prOviding tHe clOse SpaTiaL rEquirEmEnts FOr coNjugAtion. trAnsFormatioN is aLso frequenTLY obserVEd in bIOfilms. baCterIAl autolysis iS a key MechAnisM In biOfIlm sTructurAl rEGUlation, PrOVidiNg aN AbUndANt SOuRCE oF competenT Dna PRimeD FOR transformATive uptaKe. in sOme iNstaNces, InTEr-BiofiLM QUoRUm sensING Can enhanCe the CoMPeTeNce oF fReE FloaTInG ednA, furtHer pRomoting transforMatiOn. Stx geNe TraNsFeR tHrough BacteriOphaGe CArRIeRs haS beEn WitnesSeD wItHIn BiofilMS, which sUgGESTs that bIofilms arE aLso a suItAblE EnvirONment FOr TrAnsdUctIon. membrAne VEsicleS hgt occurs when ReLEased meMBrane veSiCles (cOntaining Genetic InforMatIoN) fuse wIth A rEcIpIEnT bactERiA, AnD rELeaSE gEnetic MaterIal intO tHe BACtERIa's CyToplaSm. recent researcH has revealeD thAt mEmBRANe VESicLE hgt can promotE siNGle-STRaiN bIOfiLM FoRmATion, yet tHe rOle meMbrane vesIcle hGt pLaYs In THe fOrmatioN of Multistrain bioFilmS iS sTiLl unKnown. gtas, or GenE transfER agentS, Are phaGE-liKe parTIclEs pRodUcEd By the host bacTeRia anD cOnTain random dna fragmENts FROm THe hOst bActerIa GEnomE. Hgt wItHin bioFIlmS Can conFer anTIbiotIc RESistaNce or INCReaseD PathOgenIcitY AcroSs thE BioFilmS' POpulAtiOn, PromOTIng bIofiLm hoMEostAsIS.