Bacterial gene transfer

Horizontal Gene Transfer: Transposons

"Jumping Genes" First identified by Barbara McClintock in maize (Nobel Prize: 1983) Some transposons able to move in and out of chromosome or plasmid Transposons often contain antibiotic resistance genes

What if the plasmid had antibiotic resistance genes? (GN)

now you have two. Conjugation is the 1# of moving resistance genes trough population. Plus you are transferring a plasmid. Why they are different shapes -> conjugation can occur bw different species

Conjugation

-Direct transfer of DNA (plasmid) from a donor cell to a recipient (direct contact) -Both cells can conjugate with others (GN) -Efficient way of getting genes -Passage of antibiotic resistance genes Conjugative pilis Donor is living (different from transformation, donor is dead) After: donor and recipient can conjugate with other cells. # 1 way antibiotic resistance spread!!

Can conjugation occur bw gram negative and positive?

-NO bw gram negative and gram negative gram positive and gram positive? Yes!!!

Conjugated pilus.

Direct contact bw two living cells, after that contact is made there is a copy that was sent from donor to recipient We know that the bacteria on the left is the donor, and it producing a long conjugated pilus that attached to the receptive. If we let that progress, the pilus makes them do contact, then copy is transfer from donor to recipient.

Horizontal gene transfer conjugation - Gram positive

Donor to recipient, with their chromosome and plasmid. The recipient forms signaling molecules referred as pheromones (different geometrical shapes, 3 different signals). What is involved in pheromone? chemical attractants that a lot of organism produce and bring them together. (bacteria produce them to attract a mate) The recipient wants to attract a mate that has plasmids that responds to those there pheromones. So the donor senses the pheromone. Wow triangle pheromone! So what happens is the two get together (no pilus, it has sticky proteins) what happens? A copy of the tringle gets pass to the recipient. Once the has the triangle production and now it has the pheromone of the square and circle.

Gram Positive

Enterocoucs -they love taking DNA Up! They can do Conjugation.

Transposition

Fragments of DNA called transposons (Tn) They can jump around from chromosome to plasma How corn differ in color - why there are so many different colors? -fragments were jumping and that resulted in different colors Tn can encase from the plasmid and put himself into the chromosome of the bacteria cell. Bacteria replicates the DNA and pass the Antibiotic resistance (some can move as a whole in put themselves on the DNA molecule and some others can leave a copy behind and insert other in the chromosome)

Hypothetical mechanism of antibiotic resistance

Hypothetical mechanism -An enterococcus cells has the vancomycin resistance gene. Those genes are also located in a tranponson. -S. aureus has it's own plasmid. -Conjugation -transposition Two genes ( incompatibility). Before the plasma gets degraded, the transposons inserts itself into the right plasma. E The most common mechanism of antibiotics involve conjugation at some point (recordar!)

Transfer of Antibiotic Resistance

May involve multiple mechanisms -Conjugation -Trasposition -Transformation Example: Vancomycin resistance -from E. faecalis to S. aureus Most common mechanisms involve conjugation

vertical (adaptation through gene transfer)

Mutation passed on to progeny Mutation of the genetic info. It can pass through generation to generation and we get population with that mutation (like antibiotic resistance)

Transformation (horizontal gene transfer)

Recipient cell takes up "free" DNA from lysed donor cell Recipient must be competent Donor DNA inserted in recipient chromosome First type of HGT -Circle is the chromosome -What happens to the bacteria cell, something bad and dies, so it's DNA fragments are released in to the enviroment. -The recipient cells take fragments of that DNA and incorporated into it's own genetic material, once it has it's called TRANSFOR Uptake of "naked" DNA. - Donor cell dead. Recipient is "competent" to take up DNA.

Horizontal gene transfer (conjugation) (GN)

There are no genes on the chromosome. Only Genes on the plasmid. In other words, the plasmid is directing its own transport (called the F plasmid for fertility). IF the donor has the F plasmid is refers as F+ cell (it has that ability to conjugate with other cell) The recipient receive the F- (worst grade) Donor starts to produce the conjugative pilus (build of individuals proteins that extend from the donor which is codded by the F plasmid) The pilus contracts and directs the recipient with direct contact with the donor. There is an opening bw the two cells, what passes through there? The donors give a copy (keeps one for self) and one for the recipient. The cell envelop seals themselves up and separate Now the recipient has a copy of the fertility plasmid and can go and conjugate by itself!!

Horizontal (adaptation through gene transfer)

Transfer of genetic material (plasmid) bw cells - Cell has DNA and plasmid (can have the ability to transfer their copies) the plasmid hops to the next cell and the recipient have the new plasmid. That plasmid can be transmitted through generation vertically, which makes a new population. Important in terms in antibiotic resistance.

Competent

recepient has to be C (naturally or artificually induced) in order for the DNA chromosome to be inserted E. Coli cells are shock to be made C

Recipient is "competent" to take up DNA.

some bacteria cells are naturally C, it's part of their own growth cell. When it becomes C (if is not naturally C) so they become in stationary phase. What controls C in this kind of bacteria? QUORUM SENSUM phenomenon. bacillus and streptococcus can do this. Both are gram positive. Neisseria (gram negative). -E. coli can be transformed chemically (not naturally C) we need to chemical induce them with heat shock, voltage, etc.

Experiment

streptococcus pneumoniae A "S" strain: had really smooth colony type and the cells produce a capsule (capsule-producing) This strain is virulent, so the mouse got pneumonia and die! X.X B He also had a second called R strand "R" strain: it had Rough colonies They did not produce a capsule And when you injected that into a mouse, the mouse was fine!! -> AVIRULENT C He killed the virulent bacteria, then it injected and the mouse didn't die D He mixed the heat killed bacteria W/ the R and the mouse didn't survive this time. -The culture the pneumococcus of the mouse, he found living R strain and living S strain!!! How you explain this? -> the R strain picked the DNA of the heat killed S, the genes that have the information for producing the capsule!! This example shows from streptococcus One things that affects transformation is that occurs in very similar bacteria (both strepto) in the lab we can change that rule. So in nature it limited (restricted). They need to be related. The DNA can conbine together because they are similar ins sequence. When it is integrated the recipient can show those genes.