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By

Prof. Dr. Asem Shehabi and Dr. Suzan Matar

Bacterial GeneticsBacterial Genetics

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Bacterial Genes-1Bacterial Genes-1 All patterns of growth, All patterns of growth,

metabolism, essential cellular metabolism, essential cellular structures, biological structures, biological characteristics of bacteria are characteristics of bacteria are controlled by controlled by DNA encoded & DNA encoded & expressed genes. expressed genes.

Bacterial GenomeBacterial Genome: : Chromosome, Chromosome, single circular single circular double-stranded DNA.double-stranded DNA.

1300 um long contains 1300 um long contains 2-5 x 102-5 x 1066 nucleotide bases, nucleotide bases, enough DNA to encode enough DNA to encode 1- 3 1- 3 thousand different genes. thousand different genes. According to bacteria types.According to bacteria types.

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Genetic informationGenetic information is encoded in is encoded in DNADNA, , transcribed into transcribed into mRNA, mRNA, translated on translated on RibosomesRibosomes through through tRNA tRNA into various into various protein polypeptides/structures and protein polypeptides/structures and enzymes with diverse functionsenzymes with diverse functions

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GeneGene:: A segment of DNA specifies production of a A segment of DNA specifies production of a particular amino acid, polypeptide chain function particular amino acid, polypeptide chain function (Enzyme, Protein)(Enzyme, Protein)

Bacteria with similar organization and location of Bacteria with similar organization and location of essential genes are grouped within the same Family- essential genes are grouped within the same Family- Genus-Species- strains.Genus-Species- strains.

The sequence analysis of bacterial genomes has The sequence analysis of bacterial genomes has confirmed that confirmed that genetic change / mutationgenetic change / mutation in bacteria in bacteria occurs both by alteration of the DNA base sequence, occurs both by alteration of the DNA base sequence, gain, lossgain, loss or or substitutionsubstitution of one base pairs or of one base pairs or more..Small/larger DNA segments containing genes. more..Small/larger DNA segments containing genes.

Bacterial genome includes Chromosome & DNA Bacterial genome includes Chromosome & DNA Plasmid, DNA / RNA Bacteriophage Plasmid, DNA / RNA Bacteriophage

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Bacterial Genes-2Bacterial Genes-2

The distinction between The distinction between genotype & phenotype genotype & phenotype is is fundamental to the understanding of heredity and fundamental to the understanding of heredity and evolution of microorganisms. evolution of microorganisms.

Genotype / Wild Type Genotype / Wild Type : : RepresentsRepresents allall potential potential genes of bacteria cell.. Its genome.. All Inherited genes of bacteria cell.. Its genome.. All Inherited essential biological features & growth patterns.essential biological features & growth patterns.

PhenotypePhenotype:: The expressed genes..The observed The expressed genes..The observed characteristics of the of the individual bacteria characteristics of the of the individual bacteria species/strain. Expressed by physical & biochemical species/strain. Expressed by physical & biochemical properties. Growth patterns, Fermentation products, properties. Growth patterns, Fermentation products, Antibiotic resistance, Toxins production. .etc. Antibiotic resistance, Toxins production. .etc.

Bacterial bio-engineering Bacterial bio-engineering has made important has made important contributions to medicine, food agriculture & industry, contributions to medicine, food agriculture & industry, medical drugs like Insulin ,Interferon, Vaccinesmedical drugs like Insulin ,Interferon, Vaccines

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Lab diagnosis of Lab diagnosis of

pathogens:pathogens: Polymerase Chain Polymerase Chain

Reaction (PCR Reaction (PCR technique) .. technique) .. allows allows amplification of specific amplification of specific region of DNA to detect region of DNA to detect few number of few number of microorganism/ cell DNA microorganism/ cell DNA in clinical specimens.. in clinical specimens.. Blood, Urine.. identify Blood, Urine.. identify cause of Disease .. cause of Disease .. Bacteria, Viruses & othersBacteria, Viruses & others

16S ribosomal RNA gene 16S ribosomal RNA gene (16srRNA) is highly stable (16srRNA) is highly stable in most bacterial typesin most bacterial types

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Plasmid:Plasmid:    - Extra-chromosomal piece of circular double-Extra-chromosomal piece of circular double-

stranded autonomous DNA stranded autonomous DNA - Replicate by itselfReplicate by itself- It often carries It often carries nonessential genes nonessential genes such as such as

resistance to antibiotics, virulence factors resistance to antibiotics, virulence factors (bacteriocin, enterotoxin, adhesion factor).(bacteriocin, enterotoxin, adhesion factor).

Plasmids vary in size (1 to over 1,000 kilobase -Plasmids vary in size (1 to over 1,000 kilobase -pairs (kbp), copy number and host range (1-pairs (kbp), copy number and host range (1-1000).. Each contains 1000).. Each contains 5-100 genes5-100 genes.. Bacterial cell .. Bacterial cell contains1-10 plasmids.contains1-10 plasmids.

Simple PlasmidSimple Plasmid

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Types of PlasmidsTypes of Plasmids

1. 1. Conjugative plasmidConjugative plasmid: : A plasmid capable of A plasmid capable of transmitting itself between bacteria.transmitting itself between bacteria.

F-plasmid: F-plasmid: F-factor PlasmidF-factor Plasmid Fertility. F Fertility. F++, F , F --,,

Produces Pilus. Produces Pilus.

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2. Nonconjugative plasmid: 2. Nonconjugative plasmid: Carried & transmitted by a conjugative plasmid Carried & transmitted by a conjugative plasmid

between bacterial cells. between bacterial cells.

33 . .Transposones / integronsTransposones / integrons::  (jumping genes)  (jumping genes)

Nonessential small genetic elements that can exist in Nonessential small genetic elements that can exist in two ways in the bacterial cell: Both can be two ways in the bacterial cell: Both can be integrated into the bacterial chromosome or integrated into the bacterial chromosome or attached to plasmid in the cytoplasmattached to plasmid in the cytoplasm

chromosome plasmid

transposon

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Broad Host Range PlasmidBroad Host Range Plasmid:  :  - Capable of replication in many unrelated bacteria.. - Capable of replication in many unrelated bacteria..

different genera.. Species.. different genera.. Species.. E.coli ,Salmonella-E.coli ,Salmonella-PseudomonasPseudomonas.. etc. contribute to spread antibiotic .. etc. contribute to spread antibiotic resistance within short time. resistance within short time.

Narrow Host Range PlasmidNarrow Host Range Plasmid::  Only capable of   Only capable of replication in a single bacteria species. replication in a single bacteria species. E.coli , E.coli , Staphylococcus Staphylococcus speciesspecies or very closely related or very closely related bacteria species.bacteria species.

DonorDonor bacterial cell (bacterial cell (FF++ ) ) that donates some of its that donates some of its DNA to another cellDNA to another cell.. F.. F++ Cell Cell

RecipientRecipient bacterial cell (bacterial cell (FF- - ))that receives DNA from that receives DNA from the donor cell.the donor cell.

Gene Transfer is common in most Bacteria.. Emerge Gene Transfer is common in most Bacteria.. Emerge of new pathogenic strains.. of new pathogenic strains.. R-strains, Toxic/virulent R-strains, Toxic/virulent strains etc.strains etc.

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Genetic Change in BacteriaGenetic Change in Bacteria Genetic changes/MutationGenetic changes/Mutation .. A major mechanism for the .. A major mechanism for the

appearance of new pathogens/toxigenic strains. development appearance of new pathogens/toxigenic strains. development of antimicrobial resistance.. can occur and become widespread of antimicrobial resistance.. can occur and become widespread over a short period of time over a short period of time

MutationMutation affects the epidemiology & virulence of a pathogen.. affects the epidemiology & virulence of a pathogen.. contribute to changes in the nature and prevalence of certain contribute to changes in the nature and prevalence of certain important infections. important infections.

Genetic variationGenetic variation in bacterial antigens (capsule, toxins) of in bacterial antigens (capsule, toxins) of some pathogens can seriously complicate the development of some pathogens can seriously complicate the development of vaccines against those organisms. vaccines against those organisms.

Genetic change accounts for the evolution of bacterial Genetic change accounts for the evolution of bacterial pathogens.. pathogens.. Complicate Treatment of InfectionsComplicate Treatment of Infections..

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Bacterial Bacterial MutationMutation There are two basic mechanisms that produce genetic There are two basic mechanisms that produce genetic

change in bacterial cells: change in bacterial cells: Natural and InducedNatural and Induced. . Mutation of existing DNA is expressed in Mutation of existing DNA is expressed in nucleotide nucleotide

sequence changessequence changes (insertions, deletions, DNA (insertions, deletions, DNA rearrangements like inversions, duplications, rearrangements like inversions, duplications, transpositions) occur mostly spontaneously at a low transpositions) occur mostly spontaneously at a low frequency of frequency of 1010-3-3 to 10 to 10-10-10 per bacterial cell per bacterial cell.. bacterial .. bacterial StrainStrain

Induced mutation Induced mutation followed mostly used chemical followed mostly used chemical agents or radiation.. A slow genetic process can agents or radiation.. A slow genetic process can develop in vivo & vitro..develop in vivo & vitro..natural /induced conditions. natural /induced conditions.

This genetic exchange process can produce dramatic This genetic exchange process can produce dramatic changes in the changes in the phenotypic propertiesphenotypic properties of an bacterial of an bacterial strain.. Development of Resistance.. Toxigenic Strains strain.. Development of Resistance.. Toxigenic Strains

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Mutation in Bacterial ChromosomeMutation in Bacterial Chromosome

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Mechanism of gene transfer between bacteriaMechanism of gene transfer between bacteria

1-Transformation:1-Transformation: the process of genetic exchange .. the process of genetic exchange .. free linear DNA released by dying bacteria .. taken up free linear DNA released by dying bacteria .. taken up by other bacterial cells and incorporated into the by other bacterial cells and incorporated into the chromosome/ plasmid by homologous recombination.chromosome/ plasmid by homologous recombination.

Only certain pathogens (Only certain pathogens (S. pneumoniaeS. pneumoniae, N. , N. gonorrhoeaegonorrhoeae ) are capable of doing this process in ) are capable of doing this process in vitro or vivo ..under natural condition.vitro or vivo ..under natural condition.

2. Conjugation: 2. Conjugation:     It occurs mostly in Gram negative It occurs mostly in Gram negative bacteria.. By presence Factor F (fertility factor).. bacteria.. By presence Factor F (fertility factor)..

F plasmid.. Contains F-factor is capable of replicating F plasmid.. Contains F-factor is capable of replicating itself.  It is also capable of transferring itself from host itself.  It is also capable of transferring itself from host to host ..conjugative plasmid. to host ..conjugative plasmid. 

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Transduction Bacteriophage:Bacteriophage:    A virus that infects bacteria.. Phage genomes consist of   A virus that infects bacteria.. Phage genomes consist of

either RNA or DNAeither RNA or DNA Each phage requires the presence of a particular receptor.. bacteria lacking Each phage requires the presence of a particular receptor.. bacteria lacking

specific receptor are immune to infection by that particular phage. specific receptor are immune to infection by that particular phage. Transduction is the process of moving bacterial DNA from one cell to

another using a bacteriophage.Bacteriophage or just “phage” are bacterial viruses. They consist of a small piece of DNA inside a protein coat. The protein coat binds to the bacterial surface, then injects the phage DNA. The phage DNA then takes over the cell’s machinery and replicates many virus particles.Two forms of transduction:

–1. Generalized: any piece of the bacterial genome can be transferred

2 .specialized: only specific pieces of the chromosome can be transferred.

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Bacteriophage StructureBacteriophage Structure

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TransductionTransduction Two types of phage infections : Two types of phage infections :  LyticLytic and and Lysogenic infection.Lysogenic infection.   Lytic / VirulentLytic / Virulent phagephage.. the phage produces progeny and lysis .. the phage produces progeny and lysis

the host cell.. the host cell.. Generalized Transduction.. Generalized Transduction.. Pick any part of Pick any part of bacterial chromosomebacterial chromosome

  Lysogenic / Temperate phageLysogenic / Temperate phage.. A phage that can enter into .. A phage that can enter into lysogeny with its host. insert lysogeny with its host. insert certain genescertain genes into bacterial into bacterial chromosome.. chromosome.. ProhageProhage .. ..

lysogenic state / lysogenylysogenic state / lysogeny.... Lysogenic conversion from nontoxigenic strain to toxogenic.. Lysogenic conversion from nontoxigenic strain to toxogenic.. C.diphtheriaC.diphtheria, , Beta-Hemolytic StreptococciBeta-Hemolytic Streptococci (Group A).. (Group A)..

Staphyloccocus aureusStaphyloccocus aureus.. production of toxins by specific .. production of toxins by specific bacteriophages.. increased virulence bacteriophages.. increased virulence

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Generalized transduction

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Detection of Lytic Cells (Plaques)Detection of Lytic Cells (Plaques)in vitro-Petri dish in vitro-Petri dish