3 heredity and variation of bacteria

Bacterial Heredity and Variation

Heredity

The biological character between parental

generation and their off-spring is basically

identical, and the character can inherits from

generation to generation stationary.

The basic principle of heredity and variation

Variation

In general the term variation means the

difference in characteristics of organisms

belonging to the same species in a natural

population.

It contains genotypical variation and phenotypical variation

Section 1 bacteria variation

Morphological and Structure VariationMorphological and Structure Variation

a bacterial spheroplast or protoplast originating from a normal bacterium following partial or complete removal of the cell wall.

Variation of bacteriaVariation of bacteriaVariation in morphology and structureVariation in morphology and structure lose capsule (Pneumococcus)lose capsule (Pneumococcus) H-OH-O Lose SporeLose Spore L-formL-form

Variation Variation

Variation in virulenceVariation in virulence Bovine TBBovine TB--BCGBCG

13years, 230 generation13years, 230 generation

Bacillus diphtheriaeBacillus diphtheriae infected by infected by corynebacteriophage: corynebacteriophage: Virulence Virulence ↑

corynebacteriophage

Virulent strainavirulent strain

VariationVariation

Variation in drug resistanceVariation in drug resistance Penicillin resistant strains of Penicillin resistant strains of staphstaph

ylococcusylococcus aureusaureus

Variation in enzyme activityPhenotypicGenotypic

•Bacterial chromosomeBacterial chromosome

•PlasmidPlasmid

•Bacteriophage Bacteriophage

•Transposable elementsTransposable elements

Section 2 Bacterial Genetic Elements

The characteristic of bacterial genome:

A. Covalently closed circular DNA, naked

nucleic acid molecular and without histone.

B. Operon structure

C. No intron, not need splicing after

transcription

D. There is no overlap in structural gene.

Bacterial chromosomeBacterial chromosome

The structure of operon

exon

modulating sequence

promoter

operator

The characteristic of bacterial genome:

A. Covalently closed circular DNA, naked

nucleic acid molecular without histone.

B. Operon structure

C. No intron, not need splicing after

transcription

D. There is no overlap in structural gene.

SizeSize E.coliE.coli 1300 1300m, 4288genm, 4288gen

ee

Rolling-circle pattern of Rolling-circle pattern of replication replication


•PlasmidPlasmid




Concept:

A circular, double-stranded

unit of DNA that replicates

within a cell independently of

the chromosomal DNA.

Plasmids are most often found

in bacteria and are used in

recombinant DNA research to

transfer genes between cells.

PlasmidPlasmid

1.According to transfer properties1.According to transfer properties

Conjugative plasmidsConjugative plasmids:: ConjugativeConjugative plasmids contain so- plasmids contain so-

called called transfertransfer genesgenes, which perform the complex process , which perform the complex process

of of conjugationconjugation, the sexual transfer of plasmids to another , the sexual transfer of plasmids to another

bacteriumbacterium

Nonconjugative plasmids:Nonconjugative plasmids: Non-conjugativeNon-conjugative plasmids are plasmids are

incapable of initiating conjugation, and therefore, their incapable of initiating conjugation, and therefore, their

movement to another bacterium, they must be transferred movement to another bacterium, they must be transferred

together with conjugative plasmids, during conjugation.together with conjugative plasmids, during conjugation.

ClassificationClassification

• self-duplication, it is a replicon.• The products encoded by plasmids assign the host bacteria some characteristics, such as drug resistance, pathogenicity, etc.• It can be removed naturally. The rate of natural remove of plasmids is about 10-2 ～ 10-8, and it can be removed by treatment with mega temperature, ultraviolet rays, etc.

The The characteristic of plasmids ：：

Transitivity ： Conjugative plasmids —— transfer by

sexual pili

Nonconjugative plasmids——transferred

together with conjugative or phage.

2.According to Genetic Information2.According to Genetic Information

Fertility plasmid (F factor)

————which contain only transferwhich contain only transfer genes. genes.

Their only function is to initiate conjugation.Their only function is to initiate conjugation.

Resistance plasmids （ R factors)

which contain genes that can build a

resistance against antibiotics or poisons.

Historically known as R-factors, before the

nature of plasmids was understood.

Tn 9

Tn

21

Tn 10Tn 8

RTF

R determinant

RTFRTF( ( resistance transfer factor)

■ ■ Conjugative plasmidConjugative plasmid

■ ■ Transfer genesTransfer genes

R determinantR determinant

■■ Resistance genesResistance genes

■■ TransposonsTransposons

Virulence plasmids, which turn the bacterium

into a pathogen.

Metabolism plasmids, which enable the

digestion of unusual substances, e.g., salicylic

acid.


•PlasmidPlasmid




Bacteriophage or phageBacteriophage or phage

Obligate intracellular parasites that

multiply inside bacteria , fungi, actinomycetes

or sprirochete by making use of some or all of

the host biosynthetic machinery. Also called

phage, or bacterial virus.

Definition:

1. Morphous and sturcture ： The appearance of most phages likes a

tadpole, while the other’s likes a ball or

minute bar. 2. Chemical composition ： nucleic acid (genetic material)——dsDNA ssDNA +/- ssRNA dsRNA Proteins——mainly found in capsid.

T4 bacteriophages infecting T4 bacteriophages infecting E.coliE.coli..

TailTail Tail collarTail collar Tail Tail Sheath Tail core Tail core Tail plateTail plate

Tail pins Tail fiber

HeadCore （ nucleic acid ）Capsid （ proteins ）

phage

The appearance of E.coli T4 phage (TEM×390,000)(TEM×390,000)

3. Classification3. Classification

According toAccording to The fate of host bacteria infected The fate of host bacteria infected

with phagewith phage

① ① virulent phage

Phage that can only multiply within bacteria

and kill the cell by lysis.

Characteristics:Characteristics:

aa 、、 Large scaleLarge scale proliferate in host cell cell

bb 、、 Split or lyse host bacteriaSplit or lyse host bacteria

cc 、、 Progeny Progeny Phage can infect other can infect other

sensitive cell, thus sensitive cell, thus bacteriolysis cyclebacteriolysis cycle

established.established.

②② Lysogenic or temperate phage

Phage that can either multiply via the

lytic cycle or enter a quiescent state in the

bacterial cell.

• Prophage

• Lysogen

Prophage: A prophage is a phage genome inserted as

part of the linear structure of the DNA chromosome of a

bacterium. Prophages are important agents of horizontal

gene transfer.

Lysogen (Lysogenic bacteria): a bacterium which

contains in its genome the DNA of a virus which is lying

dormant, passively letting itself be replicated by the

bacterium whenever the bacterium replicates its own

genome (a lysogenic virus), but able to reactivate and

destroy the bacterium at a time of the virus's choosing

(becomes a lytic virus).

1. The division of host cell is normal, and the

genome of phage is inherit to daughter cell

2. The host cell bear the competence of immunity

to infect with relative phage.

3. The integrated prophage bring some new

characters to its host cell.

4. The phage genome will deprive and enter to the

lytic cycle spontaneously or induced by some

factors, result in the lysis of the host cell.

The characters of lysogenic bacteria

Significance of LysogenySignificance of Lysogeny

Lysogenic conversionLysogenic conversion

Toxin production by Toxin production by Corynebacterium Corynebacterium

diphtheriaediphtheriae

avirulent strain Virulent strain

corynebacteriophage


•PlasmidPlasmid




Transposable elementsTransposable elements

Transposable elements are a heterogeneous class

of genetic elements that can insert at new locations on

chromosomes, plasmids and phages without the

limitation of homologous recombination , it is also

called jumping genes or movable genes.

Definition

Nature ： DNA sequences in bacteria cell that

can change its position.

Transfer way ： The transfer or shift of the transposable transposable

element element was resulted by special recombinase

coded by its own DNA sequence.

ClassificationClassification ：：

• Insertion sequenceInsertion sequence （（ ISIS）） • TransposonTransposon （（ TnTn）） • Bacteriophage MuBacteriophage Mu

1.1. Insertion sequenceInsertion sequence （（ ISIS ））

DefinitionDefinition

Insertion sequences are transposable genetic Insertion sequences are transposable genetic

elements that carry only genes that are elements that carry only genes that are

required for transposition.required for transposition.

StructureStructure

Insertion sequences are small stretches of Insertion sequences are small stretches of

DNA that have repeated sequences at their endsDNA that have repeated sequences at their ends , ,

which are involved in transposition. In between which are involved in transposition. In between

the terminal repeated sequences there are genes the terminal repeated sequences there are genes

involved in transposition and sequences that can involved in transposition and sequences that can

control the expression of the genes but no other control the expression of the genes but no other

nonessential genes are present.nonessential genes are present.

2. Transposon2. Transposon （（ TnTn ））

DefinitionDefinition

Transposons are transposable Transposons are transposable

genetic elements that carry one or more genetic elements that carry one or more

other genes in addition to those for other genes in addition to those for

transposition.transposition.

StructureStructure

The structure of a transposon is similar to The structure of a transposon is similar to

that of an insertion sequence. The extra genes that of an insertion sequence. The extra genes

are located between the terminal repeated are located between the terminal repeated

sequences. In some instances (composite sequences. In some instances (composite

transposons) the terminal repeated sequences transposons) the terminal repeated sequences

are actually insertion sequences.are actually insertion sequences.

IR IRTransposase Gene Extra genes

ImportanceImportance Many antibiotic resistance genes are located on Many antibiotic resistance genes are located on transposons. Since transposons can jump from one transposons. Since transposons can jump from one DNA molecule to another, these antibiotic DNA molecule to another, these antibiotic resistance transposons are a major factor in the resistance transposons are a major factor in the development of plasmids which can confer development of plasmids which can confer multiple drug resistance on a bacterium harboring multiple drug resistance on a bacterium harboring such a plasmid. These multiple drug resistance such a plasmid. These multiple drug resistance plasmids have become a major medical problem plasmids have become a major medical problem because the indiscriminate use of antibiotics have because the indiscriminate use of antibiotics have provided a selective advantage for bacteria provided a selective advantage for bacteria harboring these plasmids.harboring these plasmids.

3 Transposable phage

Transposable phage is a temperate phage

with the competence of transposition

Section 3 The mechanisms of bacterial variation

variation

Genotype variation

Phenotype variation

Gene mutation

Chromosome aberration

Gene recombination

Gene transfer and recombinationGene transfer and recombination

Basic conceptBasic concept

Gene transfer :Gene transfer :

The process that DNA transfer from donor to The process that DNA transfer from donor to

recipient.recipient.

Gene recombination :Gene recombination :

The process that The process that exogenous DNA integrate with

the chromosome of the recipientrecipient cell , result in the

change of the genotype and become a recombinant

bacteria.

The main ways of gene transfer and

recombination ： Transformation

Conjugation

Transduction

Lysogenic conversion

Protoplast fusion

TransformationTransformation

Definition:Definition:

Transformation is gene transfer from the Transformation is gene transfer from the

donor cell DNA to a recipient cell. Certain donor cell DNA to a recipient cell. Certain

bacteria (bacteria (e.g.e.g. Bacillus, Haemophilus, Neisseria, Bacillus, Haemophilus, Neisseria,

Pneumococcus) can take up DNA from the Pneumococcus) can take up DNA from the

environment and the DNA that is taken up can environment and the DNA that is taken up can

be incorporated into the recipient's chromosome.be incorporated into the recipient's chromosome.

Injection

Bacterialcolonies

Rough nonvirulent(strain R)

Results

Mouse healthy

Smooth virulent(strain S)

Mouse dies

Heat-killedsmooth virulent(strain S)

Live strain S bacteriain blood samplefrom dead mouse

Mouse diesMouse healthy

+

Rough nonvirulent(strain R)

Heat-killedsmooth virulent(strain S)

Griffith’s experiment identifying the “transforming principle”

Pneumococcus transformation experiment

The mechanism of transformation

Uptake of DNA bacteriolysis Recombination



Conjugation

Transduction


Protoplast fusion

TransductionTransduction


Transduction is defined as the transfer of Transduction is defined as the transfer of

genetic information between cells through the genetic information between cells through the

mediation of phage particle. mediation of phage particle.

TypesTypes of transduction: of transduction:

Generalized transductionGeneralized transduction

Transduction in which potentially any dornor Transduction in which potentially any dornor

bacterial gene can be transferredbacterial gene can be transferred

Specialized transduction

Transduction in which only certain donor

genes can be transferred

• Infection of Donor• Phage replication and degradation of host DNA•Assembly of phages particlesAssembly of phages particles• Release of phageRelease of phage• Infection of recipientInfection of recipient•Homologous recombinationHomologous recombination 　　

Potentially any donor gene can be transferred

Generalized TransductionGeneralized Transduction

The fate of exogenous DNA in Generalized Transduction:1) Complete transduction2) Abortive transduction

Bacteria DNA

Lytic bacterium

Complete transduction Abortive transduction

phage DNA

Infected by phage

integration Withoutintegration

• It is relatively easy. It is relatively easy.

• It is rather efficient, using the correct phage. It is rather efficient, using the correct phage.

• It moves only a small part of the chromosome It moves only a small part of the chromosome

which allows you to change part of a strain's which allows you to change part of a strain's

genotype without affecting the rest of the genotype without affecting the rest of the

chromosome. chromosome.

• The high frequency of transfer and the small The high frequency of transfer and the small

region transferred allows fine-structure mappingregion transferred allows fine-structure mapping

The application of generalized transductionThe application of generalized transduction

•Specialized transduction transduction is transduction in is transduction in which only which only certain donorcertain donor genesgenes can be can be transferred to the recipient. transferred to the recipient. •AnAn individual phage can only transfer certain individual phage can only transfer certain genes.genes.• Specialized transduction is mediated by transduction is mediated by lysogeniclysogenic or temperate phage and the genes or temperate phage and the genes that get transferred will depend on where the that get transferred will depend on where the prophage hasprophage has inserted in the chromosome.inserted in the chromosome.

Specialized transduction （（ Lysogenic PhageLysogenic Phage ））

Excision of the Excision of the

prophageprophage

• Replication and Replication and

release of phagerelease of phage

• Infection of the Infection of the

recipientrecipient

• Lysogenization of Lysogenization of

the recipientthe recipient

• Homologous Homologous

recombination also recombination also

possiblepossible

The mechanism of The mechanism of Specialized transduction transduction

generalizedgeneralized Specialized

Vector virulent phage

or temperate phage in

lytic cycle

temperate phage

Target gene Any dornor geneAny dornor gene Certain donor gene

Time Bacteriolysis phase Lysogenic phase

Cause Error assemble Error excisionexcision

Difference between generalized transduction generalized transduction

and and Restricted transduction transduction



Conjugation

Transduction


Protoplast fusion

Lysogenic ConversionLysogenic Conversion


The prophage DNA as a gene recombined The prophage DNA as a gene recombined

with chromosome of host cell and assign some with chromosome of host cell and assign some

character to the host cell.character to the host cell.

Example

Corynebacterium diphtheriae (Does not produce diphthera toxin)

β-corynebacteria phageInfected with

Losogenic Corynebacterium diphtheriae

(Phage’S DNA integrated into host chromosome

and encode diphthera toxin)



Conjugation

Transduction


Protoplast fusion

ConjugationConjugation


Transfer of DNA from a donor to a Transfer of DNA from a donor to a

recipient by direct physical contact between therecipient by direct physical contact between the

cells. In bacteria there are two mating types a cells. In bacteria there are two mating types a

donor (male) and a recipient (female) and the donor (male) and a recipient (female) and the

directiondirection of transfer of genetic material is one of transfer of genetic material is one

way; DNA is transferred from a donor to a way; DNA is transferred from a donor to a

recipient.recipient.

1.Conjugation of F plasmid

The basic knowledge of F factor• Function——encode sex pili• Exist form:

F+ bacteria——contain free F plasmid

F’ bacteria——contain F plasmid with some host

gene

Hfr bacteria——(high frequency recombinant)

F plasmid is integrate in host chromosome.

F- F+

HfrF’

Conjugate with F+

CuringIn

tegrate

excision

Deviational excision

Curing

Integrate

Conjugate with F’

Transform of F plasmid

Autonomous (FAutonomous (F++))

Characteristics of FCharacteristics of F++ × F × F-- crosses: crosses:

• FF-- becomes F becomes F+ + while Fwhile F++ remains F remains F++

• Low transfer of donor chromosomal genesLow transfer of donor chromosomal genes

Physiological States of F FactorPhysiological States of F Factor

Physiological States of F FactorPhysiological States of F Factor

Integrated (Hfr)Integrated (Hfr) Characteristics of Characteristics of HfrHfr × F- crosses:× F- crosses:• FF-- rarely becomes Hfr while Hfr remains Hfr rarely becomes Hfr while Hfr remains Hfr• High transfer of certain donor chromosomal genesHigh transfer of certain donor chromosomal genes

Physiological States of F FactorPhysiological States of F Factor Autonomous with donor genes (F’)Autonomous with donor genes (F’)

Characteristics of F’ x F- crosses:Characteristics of F’ x F- crosses:• F- becomes F’ while F’ remains F’F- becomes F’ while F’ remains F’• High transfer of donor genes on F’ and low High transfer of donor genes on F’ and low

transfer of other donor chromosomal genestransfer of other donor chromosomal genes

Structure of R FactorsStructure of R Factors

RTF (resistance transfer factor) Conjugative plasmidConjugative plasmid Transfer genesTransfer genes

Tn 9

Tn

21

Tn 10

Tn 8

RTF

R determinant

R determinantR determinant Resistance Resistance

genesgenes TransposonsTransposons



Conjugation

Transduction


Protoplast fusion

Protoplast fusion is a highly efficient method

for the direct transfer of expression vectors

from bacteria to other cell. It involves digesting

bacterial cell walls with lysozyme or penicilin to

produce protoplasts and then fusing the two

protoplasts in the presence of polyethylene

glycol.

Protoplast fusionProtoplast fusion

The protocol of Protoplast fusionProtoplast fusion

Bacteria A Bacteria B

Treat with lysozyme or penicilin

Protoplast A Protoplast BProtoplast A Protoplast B

Treat with polyethylene glycol

Recombinant fusion

Incubation

Recombinant bacteria

Comparison among different ways of bacterial gene

transfer and recombanation

manner Origin of gene Transfer mechanism

transformation Donor Intake directly

Generalized transduction Lysogenic bacteria virulent phage or temperate

phage in lytic cycle

Restricted transduction Lysogenic bacteria Defective phage infection

Lysogenic Conversion Temperate phage Temperate phage infection

Conjugation “Male” bacteria Sex pili communication

Protoplast fusion Protoplast Protoplast fusion

Practical implicationsPractical implicationsApplication in diagnosis, treatment anApplication in diagnosis, treatment an

d d prevention of infectious diseasesprevention of infectious diseases Eg. L-formEg. L-form

PCRPCRDetection of mutagenicityDetection of mutagenicity

Application in genetic engineeringApplication in genetic engineering

The Ames Test for mutagenicity

Summary

• Definitions: phage, prophage, transformation, conjugation,

transduction, lysogenic conversion

• bacteria

• The forms of genetic recombination

SummarySummary1.Phage 2.Transposable elements1.Phage 2.Transposable elements3.Lytic or virulent phage 4.Lysogenic or temperate phage3.Lytic or virulent phage 4.Lysogenic or temperate phage5.Transformation 6.Transduction5.Transformation 6.Transduction7.Conjugation 8.Lysogenic conversion7.Conjugation 8.Lysogenic conversion9.Protoplast fusion 10.Ames Test9.Protoplast fusion 10.Ames Test11.11. Briefly describe Briefly describe types of genetic materials in bacteria . types of genetic materials in bacteria .

1122 .Briefly describe the differences between generalized.Briefly describe the differences between generalized--transduction transduction and specialized (restricted)and specialized (restricted)--transduction.transduction.

13. 13. Briefly describe the Briefly describe the forms of genetic recombination forms of genetic recombination in bacteria.in bacteria.

1144 .Describe the practical implications of bacterial heredity and variati.Describe the practical implications of bacterial heredity and variations.ons.

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3 heredity and variation of bacteria