Bacterial GeneticsBacterial Genetics

Prof. Dr. Asem ShehabiProf. Dr. Asem Shehabi

Faculty of MedicineFaculty of Medicine

University of JordanUniversity of Jordan

Bacterial Genes-1Bacterial Genes-1

All patterns of growth, metabolism, essential cellular All patterns of growth, metabolism, essential cellular structures, biological characteristics of bacteria are structures, biological characteristics of bacteria are controlled by controlled by DNA DNA encoded & expressed genesencoded & expressed genes. . Chromosome structure/sequence of nucleotidesChromosome structure/sequence of nucleotides

Bacterial GenomeBacterial Genome:: ChromosomeChromosome.. .. single circular single circular double-stranded DNAdouble-stranded DNA.. 1300 um long contains .. 1300 um long contains 2-5 x 2-5 x 101066 nucleotide basesnucleotide bases, enough DNA to encode , enough DNA to encode 1- 4 1- 4 thousand different genesthousand different genes.. According bacteria types... According bacteria types.

Genetic informationGenetic information is encoded in is encoded in DNADNA, transcribed , transcribed into into mRNAmRNA.. translated on .. translated on RibosomesRibosomes through through tRNAtRNA into various protein structures..enzymes..Functionsinto various protein structures..enzymes..Functions

3/3/ GeneGene : A segment of DNA specifies production of a : A segment of DNA specifies production of a

particular particular polypeptide chain functionpolypeptide 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 essential genes are grouped within the same Family- 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 or lossgain or loss of small/larger DNA segments containing of small/larger DNA segments containing genes. genes.

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

Mutation in Bacterial ChromosomeMutation in Bacterial Chromosome

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

Genetic manipulation by bioengineering allow to Genetic manipulation by bioengineering allow to introduce new genes or cut genes to produce new introduce new genes or cut genes to produce new clones of bacteria/strain with new properties.clones of bacteria/strain with new properties.

4/4/ Lab diagnosis of pathogens:Lab diagnosis of pathogens: Polymerase Chain Reaction (Polymerase Chain Reaction (PCR techniquePCR technique)) allows allows

amplification of amplification of specific region of DNAspecific region of DNA to detect few to detect few number of microorganism/ cell DNA in clinical number of microorganism/ cell DNA in clinical specimens.. Blood, Urine.. identify cause of Disease.specimens.. Blood, Urine.. identify cause of Disease.

Plasmid:Plasmid:    Extra-chromosomal piece of circular Extra-chromosomal piece of circular double-stranded double-stranded autonomousautonomous DNA .. replicate by itself..  DNA .. replicate by itself..  It often carries It often carries nonessential genes nonessential genes such as such as resistance to antibiotics, virulence factors (bacteriocin, resistance to antibiotics, virulence factors (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.. contain contain 5-100 genes5-100 genes.. .. Bacterial cell contains1-10 Bacterial cell contains1-10 plasmids.. saml & large.plasmids.. saml & large.

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

Types of PlasmidsTypes of Plasmids

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 small   Nonessential small

genetic elements which can exist in two ways in the genetic elements which can exist in two ways in the bacterial cell . bacterial cell .

Both can be integrated into the bacterial chromosome Both can be integrated into the bacterial chromosome or attached to Plasmid & carried by plasmids during or attached to Plasmid & carried by plasmids during growth of bacteria.growth of bacteria.

Simple transposonSimple transposon

2/2/ Transposons: Transposons: are gene sequences that can move are gene sequences that can move

from one location to another within the bacterial cell’s from one location to another within the bacterial cell’s DNA (chromosome and plasmid).. genesDNA (chromosome and plasmid).. genes.... Transfer Transfer resistanceresistance markers(genes).markers(genes).

The simplest form of a transposon is an The simplest form of a transposon is an insertion insertion sequence (IS)sequence (IS) containing only few genes required for containing only few genes required for transposition. transposition.

Integrons:Integrons: Like transposons.. smaller in Size..carry R-Like transposons.. smaller in Size..carry R-gene cassettes.. transfer resistance markers among gene cassettes.. transfer resistance markers among related and unrelated bacterial populations.. related and unrelated bacterial populations.. Normally Normally attached to Plasmid/Chromosome .attached to Plasmid/Chromosome .

Insertion sequencesInsertion sequences (IS): (IS):  are small segment of  are small segment of DNA units that can insert themselves into DNA units that can insert themselves into Plasmid/ Plasmid/ IntegronsIntegrons.... and later attached to Chromosome.. Both and later attached to Chromosome.. Both are not capable of autonomous replication.are not capable of autonomous replication.   

2/2/ 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 ,Salmonella-PseudomonasE.coli ,Salmonella-Pseudomonas.. etc. .. etc. contribute to spread antibiotic resistance within short contribute to spread antibiotic resistance within short time. 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 or very or very closely related bacteria species.closely related bacteria species.

Donor Donor bacterial cell that donates some of its DNA to bacterial cell that donates some of its DNA to another cellanother cell.. ..

Recipient Recipient bacterial cell that receives DNA from the bacterial cell that receives DNA from the donor cell.donor cell.

Gene Transfer Gene Transfer is common in most Bacteria.. Result in is common in most Bacteria.. Result in emerge of new property.. pathogenic strains.. emerge of new property.. pathogenic strains.. Antibiotic R-strains, Toxic/Virulent strains etc.Antibiotic R-strains, Toxic/Virulent strains etc.

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

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

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

Genetic variationGenetic variation may result may result in new bacterial strains in new bacterial strains additive bacterial antigens/virulence factors, increased additive bacterial antigens/virulence factors, increased pathogenic potential due to capsule ,toxins, R-factors pathogenic potential due to capsule ,toxins, R-factors

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

Bacterial Bacterial MutationMutation There are There are two basic mechanisms two basic mechanisms that produce genetic 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 transpositions) occur mostly spontaneously at a low spontaneously at a low frequency frequency of of 1010-3-3 to 10 to 10-10-10 per bacterial cell per bacterial cell growth/culture within a bacterial growth/culture within a bacterial clone/strainclone/strain

Induced mutation followed mostly used chemical Induced mutation followed mostly used chemical agents or radiation.. A slow genetic process can agents or radiation.. A slow genetic process can develop in vivo & vitro..Human and Animal intestines develop in vivo & vitro..Human and Animal intestines

This genetic exchange process can produce dramatic This genetic exchange process can produce dramatic changes in the changes in the phenotypic propertiesphenotypic properties of a bacterial of a bacterial strain.. In form Resistance or Toxigenic properties. strain.. In form Resistance or Toxigenic properties.

mechanism of gene transfer mechanism of gene transfer between bacteriabetween bacteria

1-Transformation1-Transformation:: This process occurs when free This process occurs when free linear DNA released by dying bacterial cells .. taken linear DNA released by dying bacterial cells .. taken up by other bacterial cells and incorporated into the up 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, , Neisseria Neisseria 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. Conjugation2. Conjugation: :  This process occurs mostly in Gram  This process occurs mostly in Gram negative bacteria.. By presence Factor F (carry negative bacteria.. By presence Factor F (carry fertility factor genes).. F-plasmid/ conjugative plasmid.. fertility factor genes).. F-plasmid/ conjugative plasmid.. is capable of replicating itself & transferring itself is capable of replicating itself & transferring itself from bacterial donor cell ( Ffrom bacterial donor cell ( F++ ) to recipient bacterial ) to recipient bacterial cell ( Fcell ( F--

) by conjugation. ) by conjugation. 

Transduction-1Transduction-1 BacteriophageBacteriophage: :   A virus that infects bacteria..   A virus that infects bacteria..

Phage genomes consist of either Phage genomes consist of either RNA or DNARNA or DNA. . The phage nucleic acid is packaged with The phage nucleic acid is packaged with

phage-encoded proteins that determine the phage-encoded proteins that determine the phage structure, and interact with phage structure, and interact with specific specific receptors on the bacterial cell surface to initiate receptors on the bacterial cell surface to initiate infection. infection.

Each phage requires the presence of Each phage requires the presence of a a particular receptorparticular receptor.. bacteria lacking specific .. bacteria lacking specific receptor are immune to infection by that receptor are immune to infection by that particular phage.   particular phage.  

Bateriophage StructureBateriophage Structure

Transduction-2Transduction-2 Two types of phage bacterial infections Two types of phage bacterial infections ::   Lytic Lytic & &

Lysogenic infection.Lysogenic infection.    Lytic / VirulentLytic / Virulent phagephage.. the phage produces .. the phage produces progenyprogeny

and lysis the host cell.. Generalized Transduction.. and lysis the host cell.. Generalized Transduction.. Phage attacks any part of bacterial chromosomePhage attacks any part of bacterial chromosome

  Lysogenic / Temperate phageLysogenic / Temperate phage.. When a phage can .. When a phage can insert a number of genes into bacterial chromosome.. insert a number of genes into bacterial chromosome.. ProhageProhage ..the bacterial cell clone becomes in ..the bacterial cell clone becomes in lysogenic stage/ lysogenylysogenic stage/ lysogeny

lysogenic conversion from nontoxigenic strain to lysogenic conversion from nontoxigenic strain to toxogenic.. toxogenic.. C.diphtheriaC.diphtheria, , Beta-Hemolytic StreptococciBeta-Hemolytic Streptococci (Group A).. (Group A).. Staphyloccocus aureusStaphyloccocus aureus.. production of .. production of toxins by specific bacteriophages.. increased virulence toxins by specific bacteriophages.. increased virulence

Detection of Lytic Cells (Plaques)Detection of Lytic Cells (Plaques)