Bacterial Genetics Lecture Notes PDF

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (4) H A N BACTERIAL GENETICS A -  Total genetic information in an organism.  Bacterial genome is a single copy (Haploid) circular DNA molecule forming the nucleoid.  Some bacteria have extra chro...

Level (1) - Semester (1) MICROBIOLOGY D R Z I A D M A LECTURE (4) H A N BACTERIAL GENETICS A -  Total genetic information in an organism.  Bacterial genome is a single copy (Haploid) circular DNA molecule forming the nucleoid.  Some bacteria have extra chromosomal DNA: ① Plasmid. ② Transposons.  DNA.  Function: ① Replication ② Gene Expression  RNA.  -  Pieces of DNA exist separate from the chromosome,  Contain origin of replication,  Independently replicate from the chromosome.  Carry antibiotic resistance (R Plasmid).  F plasmid (Fertility) of sex pili.  Toxins, enzymes & Bacteriocin.  Sugar fermentation (Dissimilation Plasmid).  Used as a cloning vector. - -  1.5 - 120 Kb pairs.  1-2 copies/cell.  F-plasmid.  10-15 copies/cell.  Up to 50 copies/cell.  Specifically engineered to be up to 100-200 copies/cell.  Most common form in bacteria, ds.  Transient natural form:  One strand is completely closed,  The other strand is opened.  Ds linear DNA, in some bacteria, unstable because it is attacked by exonucleases.  Have tra genes that mobilize plasmid from one cell to another by conjugation (Transmissible).  Can't be mobilized under any known conditions (Nontransmissible).  Present naturally.  have genes for their own replication & genes for some functions of cells; F- plasmid.  Naturally present.  Modified artificially to be used as a vector to introduce foreign DNA into cells. -  Transposons: extra chromosomal small pieces of DNA capable of moving itself from one location in DNA to another on the genome.  Movable elements or jumping genes.  Transposition: The process by which transposons excised & re-integrate inside DNA.  Code for drug resistance. ① Not capable of autonomous replication. ② Have special sequences at each end essential for their integration. -  Simplest smallest form.  Encodes only proteins for own transposition.  Their ends are same repeats either direct or inverted repeats.  IS 1, 3, 10.  Contain 2 IS at both ends & central piece of DNA often encodes for antibiotic resistance.  Tn 10: encodes for tetracycline resistance.  -  No IS but encodes for transposition proteins.  Carry genes for antibiotic resistance, & virulence factors.  Tn 3: carry Ampicillin resistance gene.  Transposons transfer DNA from one site on bacterial chromosome to another site or to a plasmid.  Subsequent transfer of the plasmid to another bacterium by conjugation leads to spread of antibiotic resistance.  Programmed rearrangements; N. gonorrhoeae, consists of movement of a gene from a silent storage site where the gene is not expressed to an active site where transcription & translation occur, Results in antigenic variation & immune evasion.  -  The process of moving a piece of DNA (chromosomal or plasmid) from one cell to another. ▪ Direct uptake of naked DNA by a recipient cell either naturally or artificially in the laboratory.  Lysed donor cell,  DNA is taken by recipient cell,  S. pneumoniae.  Laboratory Induced Competence: increasing permeability of cell envelope:  By adding calcium chloride solution & chilled on ice  Then heat-shocked.  By exposing the recipient cells & Plasmid to electrical field to form pores in the cell membrane (Competent Cells).  - ▪ Bacteriophage mediates DNA transfer from a lysed donor cell to recipient cell (without cell-to-cell contact). Bacteriophages: viruses infect bacteria. ▪ Enter the host cell integrating their nucleic ▪ Enter host cells & subsequently lyse & kill acid in the host genome or residing in the them, releasing phage progeny into the host cells as prophages, potentially existing surrounding environment. in a stable state for generations until induced to start a lytic cycle  In lytic cycle of Bacteriophage:  A random fragment of bacterial DNA is accidentally encapsulated in a phage protein coat in place of the phage DNA then transduced to a recipient bacteria:  When the phage infects bacterial cell & replicate → any piece of bacterial DNA can be packaged inside the phage.  After the cell lysis & release of phages it will → ① Infect another bacteria. ② Transfer the chromosomal DNA to the new recipient cell.  In lysogenic cycle of Bacteriophage (Temperate):  Only certain bacterial genes, located on the bacterial chromosome close to the prophage insertion site of the transducing phage are transduced:  The phage DNA is integrated at a specific site of bacterial DNA (specialized) then →  The integrated phage is excised with a piece of bacterial chromosome →  Infect another bacterial cell transferring this DNA into the recipient cell. - -  A form of gene transfer in which two cells come in contact & DNA is transferred from one cell (donor) to the other (recipient). ① Donor cell with F plasmid encodes for F pili needed for conjugation. ② Donor plasmid with tra gene (conjugative type). ③ More in Gram negative bacilli than Gram positive organisms.  The donor cell attached to the recipient cell by F pili forming a canal.  One strand of plasmid is moved from the recipient cell through the canal then replicating it self to form double strand transforming the recipient cell into F+ cell.  -  It can transfer a segment of  This integrated F factor create a high chromosome during excision from the frequency of recombination cell (Hfr donor cell (Hfr) to the recipient cell). chromosomal cell.  - DNA transferred from Chromosomal or one bacterium to plasmid another Any gene in generalized DNA transferred by a transduction; only virus from one cell to certain genes in another specialized transduction Naked DNA in the immediate Any DNA environment taken up by a cell Clinical Case  A microbiology Lab recovered Proteus species from an infected wound and reported that it had antibiotic resistance genes similar to genes previously isolated from Pseudomonas and Escherichia.  Can you suggest mechanisms by which Proteus species acquired this resistance? ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..…………..  - Questions ① What is a non-conjugative plasmid? A. A plasmid that cannot be replicated. B. A plasmid that cannot trigger the conjugation process. C. A plasmid that codes for toxins that kill conjugative plasmids. D. A plasmid that prevents the conjugation process from occurring. ② Transfer of DNA from donor cells into recipient cells by bacteriophage is called: A. Transformation. B. Transduction. C. Transcription. D. Conjugation. ③ List 3 functions of Plasmid. ……………………………………………………………………………..………….. ……………………………………………………………………………..………….. ……………………………………………………………………………..…………..