Microbiology slides 02 bacterial genetics

8/14/2019 Microbiology slides 02 bacterial genetics

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Bacterial GeneticsBacterial Genetics

Prof. Dr. Asem ShehabiProf. Dr. Asem Shehabi

Faculty of MedicineFaculty of MedicineUniversity of JordanUniversity of Jordan


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Bacterial Genes-1Bacterial Genes-1

All patterns of growth, metabolism, essential cellularAll patterns of growth, metabolism, essential cellularcomponents, characteristics of bacteria are controlledcomponents, characteristics of bacteria are controlledbyby encoded & expressed genesencoded & e

xpressed genes.. composed of.. composed ofDNADNAstructure.. sequence of nucleotides.. Chromosomestructure.. sequence of nucleotides.. Chromosome

Supercoiling folded DNA is expressed in thousandsSupercoiling folded DNA is expressed in thousandsof base pairs/ nucleotides (Kbp).. A-T, G-C paired byof base pairs/ nucleotides (Kbp).. A-T, G-C paired byhydrogen-bonding.hydrogen-bonding.

Genetic informationGenetic information is encoded inis encoded in DNADNA, transcribed, transcribed

intointo mRNAmRNA.. translated on.. translated on RibosomesRibosomes throughthrough tRNAtRNAinto various protein structures.into various protein structures.

Certain expressed bacterial genes are responsible toCertain expressed bacterial genes are responsible tocause disease by invasion, production specific toxins..cause disease by invasion, production specific toxins..

enzymes.. resist the action of antibiotics.enzymes.. resist the action of antibiotics.


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Bacterial Genes-2Bacterial Genes-2

GenotypeGen

otype-- PhenotypePhen

otype.. expressed in bacterial.. expressed in bacterialproperties.. Growth conditionsproperties.. Growth conditions

The field ofThe field ofbacterial geneticsbacterial genetics has made importanthas made importantcontributions to medicine, food agriculture & industry,contributions to medicine, food agriculture & industry,

medical drugs like insulin ,Interferonmedical dr

ugs like insulin ,Interferon....newnewantimicrobials, development effective vaccines..antimicrobial

s, development effective vaccines.. Lab diagnosis of pathogensLab d

iagnosis of pathogens:: Amplification ofAmplification ofspecific region of DNA can be achieved with bacteriaspecific region of DNA can be achieved with bacteria

enzymes ..Tag-polymerase.. endonucloses usingenzymes ..Tag-polymerase.. endonucloses usingPolymerase Chain Reaction /PCR.Polymerase Chain Reaction /PCR. PCR techniquePCR technique allow to detect few number ofallow to detect few number of

microorganism cell DNA in clinical specimens.. Blood,microorganism cell DNA in clinical specimens.. Blood,Urine.. identify cause of DiseaseUrine.. identify cause of Disease


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Bacteria contain single circular double-stranded DNA..Bacteria contain single circular double-stranded DNA..

chromosome..1300 um long.. itschromosome..1300 um long.. its GenomGenom containscontains 2-52-5

x 10x 1066 nucleotide basesnucleotide bases, enough DNA to encode, enough DNA to encode 1- 31- 3thousand different genes.thousand different genes.

GeneGene .. a segment of DNA specifies production of a.. a segment of DNA specifies production of a

particularparticular

polypeptide chain function

polypeptide chain function..Enzyme, Protein..Enzyme, Protein

Bacteria with similar organization and location ofBacteria 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 hasThe sequence analysis of bacterial genomes hasconfirmed thatconfirmed that genetic change / mutationgenetic change / mutation in bacteriain bacteria

occurs both by alteration of the DNA base sequence,occurs both by alteration of the DNA base sequence,

gain or lossgain or loss of small/largerof small/largerDNA segments containingDN

A segments containing

genes.

genes.


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Wild Type/Genotype strainWild T

ype/Genotype strain:: functional & potentialfunctional & potential

form/capacity of the genes in nature.. Inheritedform/capacity of the genes in nature.. Inherited

Phenotype:Phenotype:ExpressedExpressed form of genes.. Biochemicalform of genes.. Biochemical

characteristics.. Fermentation.. Resistance.. Toxins.characteristics.. Fermentation.. Resistance.. Toxins.

Plasmid:Plasmid: Extrachromosomal piece of circular double-Extrachromosomal piece of circular double-

strandedstranded autonomousautonomous DNA .. replicate by itself.. It oftenDNA .. replicate by itself.. It oftencarries nonessential genes such as resistance tocarries nonessential genes such as resistance to

antibiotics,antibiotics, virulence factorsvirulence factors (bacteriocin,(bacteriocin,

enterotoxin, adhesion factor).enterotoxin, adhesion factor).

Plasmids vary in size, copy number and host range..Plasmids vary in size, copy number and host range..containcontain 5-100 genes5-100 genes.. Bacterial cell.. Bacterial cell contains1-10contains1-10

plasmidsplasmids.. (Fig.1)... (Fig.1).


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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,

Nonconjugative plasmidNonconjugative plasmid: Carried &Transmitted by a: Carried &Transmitted by a

conjugative plasmid between bacterial cells.conjugative plasmid between bacterial cells.

Transposones/ IntegronsTransposones/ Integrons:: Nonessential smallNonessential small

genetic elements that can exist in two ways in thegenetic elements that can exist in two ways in thebacterial cell:bacterial cell:

Both can be integrated into the bacterial chromosomeBoth can be integrated into the bacterial chromosome

or attached to Plasmid in the cytoplasm..or attached to Plasmid in the cytoplasm..


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Fig.1- A simple PlasmidFig.1- A simple Plasmid


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6/6/ Broad Host Range PlasmidBroad Host Range Plasmid: Capable of replication: Capable of replication

in many unrelated bacteria.. different genera..in many unrelated bacteria.. different genera..

Species..Species.. E.coli to Salmonella-PseudomonasE.coli to Salmonella-Pseudomonas.. etc... etc.contribute to spread antibiotic resistance within shortcontribute to spread antibiotic resistance within shorttime.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.coliE.colior veryor veryclosely related bacteria species..closely related bacteria species..

DonorDonor:: bacterial cell that donates some of its DNA tobacterial cell that donates some of its DNA toanother cellanother cell....

Recipient:Recipient: bacterial cell that receives DNA from thebacterial cell that receives DNA from thedonor celldonor cell

Gene Transfer is common in most Bacteria.. EmergeGene Transfer is common in most Bacteria.. Emergeof new pathogenic strains.. R-strains, Toxic-strainsof new pathogenic strains.. R-strains, Toxic-strainsetc.etc.


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Transposons:Transposons:are gene sequences that can moveare gene sequences that can movefrom one location to another within the bacterial cellsfrom one location to another within the bacterial cells

DNA (chromosome and plasmid).. genesDNA (chromosome and plasmid).. genes....TransferTransferresistanceresistance markers/ genesmarkers/ genes.. The simplest form of a transposon is an insertionThe simplest form of a transposon is an insertion

sequence (IS) containing only those genes requiredsequence (IS) containing only those genes required

for transposition.. Carry transposase genesfor transposition.. Carry transposase genes Integrons:Integrons: Like transposons.. Smaller in Size..CarryLike transposons.. Smaller in Size..Carry

R-gene cassettes.. transfer resistance markers amongR-gene cassettes.. transfer resistance markers amongrelated and unrelated bacterial populations..related and unrelated bacterial populations.. Found onFound on

Plasmid/Chromosome .Plasmid/Chromosome . Insertion sequencesInsertion sequences (IS):(IS): are small segment ofare small segment of

DNA units that can insert themselves intoDNA units that can insert themselves into PlasmidPlasmid//IntegronsIntegrons.... and later attached to Chromosome.. Bothand later attached to Chromosome.. Both

are not capable of autonomous replication.are not capable of autonomous replication.


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Plasmid-TransposonsPlasmid-Transposons


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Genetic Change in BacteriaGenetic Change in Bacteria

Genetic changes/MutationGenetic changes/Mutation .. A major mechanism for.. A major mechanism forthe appearance of new pathogens. development ofthe appearance of new pathogens. development ofantimicrobial resistance.. can occur and becomeantimicrobial resistance.. can occur and becomewidespread over a short period of timewidespread over a short period of time

MutationMutation affects the epidemiology & virulence of aaffects the epidemiology & virulence of apathogen.. contribute to changes in the nature andpathogen.. contribute to changes in the nature andprevalence of certain important infections.prevalence of certain important infections.

Genetic variationGenetic variation of key bacterial antigens (capsule,of key bacterial antigens (capsule,toxins) of some pathogens has seriously complicatedtoxins) of some pathogens has seriously complicatedthe development of vaccines against those organisms.the development of vaccines against those organisms.

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


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BacterialBacterial MutationMutation

There areThere are two basic mechanismstwo basic mechanisms that produce geneticthat produce geneticchange in bacteria:change in bacteria: Natural and InducedNatural and Induced....

Mutation of existing DNA consists ofMutation of existing DNA consists ofnucleotidenucleotide

sequence changessequence changes, insertions, deletions, DNA, insertions, deletions, DNArearrangements like inversions, duplications,rearrangements like inversions, duplications,transpositions.. can occur mostly spontaneously at atranspositions.. can occur mostly spontaneously at alow frequency oflow frequency of1010-3-3 to 10to 10-10-10 per bacterial cell..per bacterial cell..

bacterial Strainbacterial Strain Acquisition of DNA from another bacterium allows theAcquisition of DNA from another bacterium allows the

recipient organism to obtain entire new genes .recipient organism to obtain entire new genes .

This genetic exchange process can produce dramaticThis genetic exchange process can produce dramatic

changes in thechanges in the phenotypic propertiesphenotypic properties of an bacterialof an bacterial


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mechanism of gene transfermechanism of gene transfer

between bacteriabetween bacteria

1. Conjugation1. Conjugation:: It occurs mostly in Gram negativeIt occurs mostly in Gram negativebacteria.. By presence Factor F (fertility factor)..bacteria.. By presence Factor F (fertility factor)..

F plasmid.. Contains F-factor is capable of replicatingF plasmid.. Contains F-factor is capable of replicating

itself. It is also capable of transferring itself from hostitself. It is also capable of transferring itself from hostto host ..conjugative plasmid.to host ..conjugative plasmid.

2-Transformation2-Transformation:: the process of genetic exchange ..the process of genetic exchange ..

free linear DNA released by dying bacteria .. taken upfree linear DNA released by dying bacteria .. taken upby other bacterial cells and incorporated into theby other bacterial cells and incorporated into thechromosome/ plasmid by homologous recombination.chromosome/ plasmid by homologous recombination.

Only certain pathogens (S. pneumoniae, N.Only certain pathogens (S. pneumoniae, 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.


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Bateriophage StructureBateriophage Structure


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Transduction-2Transduction-2

Two types of phage infections :Two types of phage infections : LyticLyticandand LysogenicLysogenicinfection.infection.

Lytic / VirulentLytic / Virulent phagephage.. the phage produces.. the phage produces progenyprogenyand lysis the host cell..and lysis the host cell.. Generalized Transduction..Generalized Transduction..

Pick any part of bacterial chromosomePick any part of bacterial chromosome Lysogenic / Temperate phageLysogenic / Temperate phage.. A phage that can.. A phage that can

enter into lysogeny with its host. insertenter into lysogeny with its host. insert certain genescertain genesinto bacterial chromosome..into bacterial chromosome.. ProhageProhage ....

lysogenic state / lysogenylysogenic state / lysogeny.. lysogenic conversion.. lysogenic conversionfrom nontoxigenic strain to toxogenic..from nontoxigenic strain to toxogenic.. C.diphtheriaC.diphtheria,,Beta-Hemolytic StreptococciBeta-Hemolytic Streptococci(Group A)..(Group A)..Staphyloccocus aureusStaphyloccocus aureus.. production of toxins by.. production of toxins by

specific bacteriophages increased virulencespecific bacteriophages increased virulence

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Microbiology slides 02 bacterial genetics