Gene transfer and applied to environmental engineering

1. Seminar Gene transfer and applied to environmental engineering Student: Luong Thi Mai Ly Prof. Chong Nuyk – Min 16 March, 2006

2. Outline • Introduction • What is transfer • How does transfer happen • The significance of transfer applied to environmental engineering

3. Pollutant -xenobiotic I.Introduction waste incineration, uncontrolled use of wood preservatives, pesticides, fungicides herbicides chlorination of drinking water, Man – made organic chemical stable, hard – to – treat, mostly toxic persistent, non – natural characteristic

4. I.Introduction Xenobiotic Environment Alien Microorganism (Bacteria,…) adapt Mutation, DNA rearrangements Horizontal gene transfer

5. I.Introduction • Horizontal gene transfer is the transfer of genes or genetic material directly from one individual cell to another by processes similar to infection • Bacteria can obtain foreign genetic materials from different sources surrounding • Genes in organic xenobiotic-degrading bacteria are often carried by Plasmids

6. Transfer to offspring vertical transfer Within this population, some are able to degrade  capable = 2 More are able to degrade due to transfer  capable = 4 Transfer to neighbor, infection  horizontal transfer II. What is transfer: kinds of transfer • Vertical gene transfer : transferring genetic material from parents to their offspring • Horizontal gene transfer exchange of genetic material among organisms of different species ……........…………………..

7. II. What is transfer: plasmid • Plasmid is a circular, double-stranded DNA molecules that is not connected to the main bacterial chromosomes and replicate independently.

8. II. What is transfer: plasmid

9. II. What is transfer: plasmid Plasmids usually contain genes, such as those coding for antibiotic resistance, conjugation, and others. Plasmid can be passed on from one bacterium to the other in a process called conjugation

10. II. What is transfer: plasmid

11. III. How does transfer happen:Mechanisms of transfer • 1. Transformation: take up free DNA from their surroundings (variety of sources: bacteria must be competent (expressing the appropriate enzymes )

12. Transformation • cell surface receptor binds to DNA • DNA is transported across the membrane • one strand of the DNA is digested away (DNA enters the cell is single stranded ) • New DNA will • recombine to the host DNA (if homologous) • simply replace a strand of the host DNA • or occur gene conversion

13. III. How does transfer happen:Mechanisms of transfer • 2. Conjugation Occurs when an organism builds a protein tube-like structure known as the F or sex pilus, joins it to its ‘‘mate’’, and transfers the genetic material ( plasmid) through the tube The F factor is Fertility plasmid - an episome that carries the genes confers the ability to conjugate upon its host cell (as well as a number of other genes) and is the genetic material transferred itself

14. Conjugation The F+ extends an F pilus toward the F- cell , when finished, temporarily connects the two cells. One strand of the F factor is nicked, begins unwinding from the other strand. The nicked strand begins to transfer through the F pilus to the F- cell and begins to be replicated

15. Conjugation • The nicked strand completely passes through to the recipient cell, and is completely replicated • This process produces a new F factor in the recipient cell, both cells are F+ . • The pilus is broken, severing the connection between the two cells Recombination rarely occurs because the F factor is not homologous to the DNA in the bacterial chromosome

16. Conjugation Involving Hfr Bacteria The Hfr bacteria cell are formed when the F factor integrates into a random position in the bacterial chromosome.  the bacterial cell is called Hfr The Hfr cell is still able to initiate conjugation with an F- cell.

17. Conjugation Involving Hfr Bacteria The Hfr cell tries to transfer the entire bacterial chromosome to the F- cell: The first: chromosomal DNA The last: F factor DNA. • Pili are fairly fragile structures, and shear forces tend to break the pilus, disrupting DNA transfer before the entire chromosome can be transferred. • The F factor is almost never transferred. Recipient cell will remain F- and new DNA can undergo recombinationwith the host chromosome or gene conversion events

18. F' Conjugation • Integrated F factors can occasionally excise themselves from the bacterial chromosome • the Hfr cell becomes an F+ again • The cell is called an F’ when the excision of the F factor from the the bacterial chromosomeis sloppy, hence it takes a small segment of the bacterial chromosome with ittake F' cells are able to initiate conjugation with F- cells because of the presence of the F factor

19. F' Conjugation When the F factor begins to transfer its DNA, it will transfer the small segment of chromosomal DNA as well. • Both cells wind up with a copy of the episome and both are F'. • The recipient cell will diploid for the segment of chromosomal DNA on the episome  is called a merozygote • The chromosomal DNA on the episome can undergo recombination with its homologous sequence on the chromosome

20. Conjugation • There is considerable evidence that distantly related prokaryotes can conjugate with one another • For example: • E. coli has been shown to conjugate with cyanobacteria • Some members of the eocytes, such as the Sulfolobales, are also capable of conjugating • Most astounding is the demonstration of E. coli conjugating with the FIG. 1. Jain et al. 490 eukaryote S. cerevisiae

21. III. How does transfer happen:Mechanisms of transfer • 3. Transduction • Transduction involves the exchange of DNA between bacteria using bacterial viruses (bacteriophage) as an intermediate • There are two types differ in their mechanism and in the DNA that gets transferred : • generalized transduction • specialized transduction

22. bacteriophage • The viral DNA is replicated numerous times, viral genes are expressed • digest the host genome into fragments • The newly replicated viral DNA molecules are packaged into viral capsids, • bacterial cell is lysed • hundreds of viral progeny are released, then go on to infect other cells phage DNA cell

23. Transduction • Generalized Transduction • a fragment of the host DNA gets packaged into a viral capsid • phage would be able to infect another cell, but it would not have any viral genes it would not be able to replicate. • The cell infected by this phage would survive, have an extra piece of bacterial DNA present

24. Transduction • Specialized Transduction establish lysogenic infection viral DNA incorporated into the host chromosome remain integrated for long time, without disturbing the cell bacteriophage (phage lambda )

25. Transduction • Specialized Transduction appropriate conditions If the infected cell survives will contain a new piece of bacterial DNA viral DNA will excise itself from the chromosome and replicates viral DNA incorporated into the host chromosome remain integrated for long time, without disturbing the cell sloppy

26. What is the agent(s) causing transfer • The basic conditions for conjugation are: • Donor cells carry a unique plasmid containing conjugation gene, responsible for the synthesis of special pili called SEX PILI. • a GATE IS OPENED between the donor and recipient cells through which DNA can pass. • A special enzyme CUTS one strand of the donor's DNA at a unique site and a newly synthesized strand of DNA • This newly synthesized strand of donor DNA is converted to a DOUBLE STRANDED

27. Transfer of genes encoding the degradation of xenobiotic allow the organisms can adapt to the presence of xenobiotics in their environment. bacteria have a powerful in degrade pollutant IV. The significance of transfer applied to environmental engineering genes encoding the degradation of organic compounds (including chlorobenzene, p-toluenesulfonate, 2,4-D, haloacetate and atrazine ) are often located on plasmids, transposons or other mobile and integrative elements. These plasmids assembled from a variety of different original sources

28. IV. The significance of transfer applied to environmental engineering horizontal exchange of catabolic genes among bacteria in microbial communities plays an important role in the evolution of catabolic pathways for many man-made chemical.  apply genes transfer to environmental engineering by controlling natural gene transfer or to use biotechnology to transfer the gene that we want has a great significance. can accelerate the degradation of pollutant .

29. IV. The significance of transfer applied to environmental engineering

30. IV. The significance of transfer applied to environmental engineering • example

31. Thank you for your attention!