Transformation, Transduction and Conjugation (Horizontal Gene Transfer in Bacteria)

there are different ways on how genes are transmitted among organisms the generic term for those subtypes is horizontal gene transfer gene transfer in general can be vertical or horizontal we speak about vertical gene transfer when the genetic material is transmitted from parent to offspring either by sexual or asexual reproduction horizontal gene transfer is gene transfer between two already existing organisms the donor transfers genetic material to a recipient organism that is not the donor's offspring we mainly distinguish between those different subtypes of the horizontal gene transfer there is transduction conjugation and transformation starting with transformation one

has to mention that this term is used for bacterial cells but also plants and other non-animal eukaryotic cells such as fungi however all examples in this video will include bacteria transformation is the uptake of free genetic material from the environment by a bacterium a bacterial cell contains the circular bacterial chromosome and in addition also extra chromosomal plasmid dna that replicates autonomously a piece of plasmid dna floating around in the environment may have been released by other bacteria the ability to take up free dna is called competence the uptake and expression of new genes can be

of selective advantage for those cells but not all bacteria are competent to take up dna by nature natural competence is restricted to a small subset of bacterial species therefore competence can also be induced by chemical modifications in the lab to transform the bacterial cell with plasmid dna containing the gene sequence of interest the cell must acquire competence one method is to use a heat shock transformation protocol calcium chloride combined with a short heat shock depolarizes the cell membrane making it permeable divalent cations especially calcium ions help to further facilitate the uptake of the negatively charged

dna in the cell the bacterial cell can express the genes on this plasmid and protein is produced another form of horizontal gene transfer is called transduction we speak about transduction when the transmission of genetic material between cells is carried out by viruses in nature this happens when a bacteriophage infects a bacterial cell the viral nucleic acid is entering the host cell and is integrated in the bacterial dna upon excision errors may occur when parts of the bacterial dna are additionally excised by accident when virus assembly takes place it may happen that bacterial host dna is

also encapsulated by accident the phages are released from its host cell this bacteriophage can infect the next cell the recipient the nucleic acid this time also containing bacterial genes again enters the cell this sequence is again integrated into the recipient's genome genes from the host cell have been successfully transferred to the recipient cell by a viral vector in the lab we use viral vectors such as lentiviruses to integrate genes of interest into the genome of eukaryotic cells another way of horizontal gene transfer between bacterial cells happens through conjugation conjugation requires cell to cell contact of

two bacteria it is unidirectional one bacterial cell is the donor the other one the recipient besides the chromosomal dna the donor contains the fertility factor a sequence found on the extra chromosomal f plasmid the donor is considered f positive the recipient however has no such f plasmid this cell is f negative f positive cells are able to form an extending structure reaching out to neighboring cells this extension is referred to as the sex pilus this protein tube attaches to the recipient cell and brings the cells together one strand of the plasmid dna passes via a

channel from the donor to the recipient after replication the double stranded dna is present in both cells in this case the recipient also contains the f factor after transfer from now on it can also be considered f positive thank you for watching make sure to subscribe and activate the notification bell if it was helpful for you you may give this video a like and also check out the channel for more scientific videos