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

VariationVariation
Variation in virulenceVariation in virulence
 Bovine TB-BCGBovine TB-BCG
13years, 230 generation13years, 230 generation

 Bacillus diphtheriaeBacillus diphtheriae infected byinfected by
corynebacteriophage:corynebacteriophage: VirulenceVirulence ↑
corynebacteriophage
Virulent strainavirulent strain

VariationVariation
Variation in drug resistanceVariation in drug resistance
 Penicillin resistant strains ofPenicillin resistant strains of staphylococcusstaphylococcus
aureusaureus
Variation in enzyme activity
Phenotypic
Genotypic

•Bacterial chromosomeBacterial chromosome
•PlasmidPlasmid
•BacteriophageBacteriophage
•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 13001300µµm, 4288genem, 4288gene
 Rolling-circle pattern ofRolling-circle pattern of
replicationreplication

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-
calledcalled transfertransfer genesgenes, which perform the complex process, which perform the complex process
ofof conjugationconjugation, the sexual transfer of plasmids to another, the sexual transfer of plasmids to another
bacteriumbacterium
Nonconjugative plasmids:Nonconjugative plasmids: Non-conjugativeNon-conjugative plasmids areplasmids are
incapable of initiating conjugation, and therefore, theirincapable of initiating conjugation, and therefore, their
movement to another bacterium, they must be transferredmovement 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.
TheThe 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.

Tn9
Tn21
Tn 10
Tn8
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.

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 infectingT4 bacteriophages infecting E.coliE.coli..

 TailTail
Tail collarTail collar
TailTail Sheath
Tail coreTail core
Tail plateTail plate
Tail pins
Tail fiber
 Head
Core （ 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 infectedThe fate of host bacteria infected
with phagewith phage
①① virulent phage
Phage that can only multiply within bacteria
and kill the cell by lysis.

Characteristics:Characteristics:
aa 、、 Large scaleLarge scale proliferate in host cellcell
bb 、、 Split or lyse host bacteriaSplit or lyse host bacteria
cc 、、 ProgenyProgeny Phage can infect othercan infect other
sensitive cell, thussensitive 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 byToxin production by CorynebacteriumCorynebacterium
diphtheriaediphtheriae
avirulent strain Virulent strain
corynebacteriophage

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 transposabletransposable
elementelement 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 geneticInsertion sequences are transposable genetic
elements that carry only genes that areelements that carry only genes that are
required for transposition.required for transposition.

StructureStructure
Insertion sequences are small stretches ofInsertion 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 betweenwhich are involved in transposition. In between
the terminal repeated sequences there are genesthe terminal repeated sequences there are genes
involved in transposition and sequences that caninvolved in transposition and sequences that can
control the expression of the genes but no othercontrol the expression of the genes but no other
nonessential genes are present.nonessential genes are present.

2. Transposon2. Transposon （（ TnTn ））
DefinitionDefinition
Transposons are transposable geneticTransposons are transposable genetic
elements that carry one or more other geneselements that carry one or more other genes
in addition to those for transposition.in addition to those for transposition.

StructureStructure
The structure of a transposon is similar toThe structure of a transposon is similar to
that of an insertion sequence. The extra genesthat of an insertion sequence. The extra genes
are located between the terminal repeatedare located between the terminal repeated
sequences. In some instances (compositesequences. In some instances (composite
transposons) the terminal repeated sequencestransposons) the terminal repeated sequences
are actually insertion sequences.are actually insertion sequences.
IR IRTransposase Gene Extra genes

ImportanceImportance
Many antibiotic resistance genes are located onMany antibiotic resistance genes are located on
transposons. Since transposons can jump from onetransposons. Since transposons can jump from one
DNA molecule to another, these antibioticDNA molecule to another, these antibiotic
resistance transposons are a major factor in theresistance transposons are a major factor in the
development of plasmids which can conferdevelopment of plasmids which can confer
multiple drug resistance on a bacterium harboringmultiple drug resistance on a bacterium harboring
such a plasmid. These multiple drug resistancesuch a plasmid. These multiple drug resistance
plasmids have become a major medical problemplasmids have become a major medical problem
because the indiscriminate use of antibiotics havebecause the indiscriminate use of antibiotics have
provided a selective advantage for bacteriaprovided 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 toThe process that DNA transfer from donor to
recipient.recipient.
Gene recombination :Gene recombination :
The process thatThe 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 theTransformation is gene transfer from the
donor cell DNA to a recipient cell. Certaindonor 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 thePneumococcus) can take up DNA from the
environment and the DNA that is taken up canenvironment and the DNA that is taken up can
be incorporated into the recipient'sbe incorporated into the recipient's
chromosome.chromosome.

Injection
Bacterial
colonies
Rough
nonvirulent
(strain R)
Results
Mouse healthy
Smooth
virulent
(strain S)
Mouse dies
Heat-killed
smooth
virulent
(strain S)
Live strain S bacteria
in blood sample
from dead mouse
Mouse diesMouse healthy
+
Rough
nonvirulent
(strain R)
Heat-killed
smooth
virulent
(strain S)
Griffith’s experiment identifying the “transforming principle
Pneumococcus transformation experiment

The mechanism of transformation
Uptake of DNAbacteriolysis Recombination

TransductionTransduction
Transduction is defined as the transfer ofTransduction is defined as the transfer of
genetic information between cells through thegenetic 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 dornorTransduction 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 transduction
2) Abortive transduction
Bacteria
DNALytic
bacterium
Complete transduction Abortive transduction
phage DNA
Infected
by phage
integration Without
integration

• 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 chromosomeIt moves only a small part of the chromosome
which allows you to change part of a strain'swhich allows you to change part of a strain's
genotype without affecting the rest of thegenotype without affecting the rest of the
chromosome.chromosome.
• The high frequency of transfer and the smallThe 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 transductiontransduction is transduction inis transduction in
which onlywhich only certain donorcertain donor genesgenes can becan be
transferred to the recipient.transferred to the recipient.
•AnAn individual phage can only transfer certainindividual phage can only transfer certain
genes.genes.
• Specialized transduction is mediated bytransduction is mediated by
lysogeniclysogenic or temperate phage and the genesor temperate phage and the genes
that get transferred will depend on where thethat 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 theExcision of the
prophageprophage
• Replication andReplication and
release of phagerelease of phage
• Infection of theInfection of the
recipientrecipient
• Lysogenization ofLysogenization of
the recipientthe recipient
• HomologousHomologous
recombination alsorecombination also
possiblepossible
The mechanism ofThe mechanism of Specialized transductiontransduction

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 transductiongeneralized transduction
andand Restricted transductiontransduction

Lysogenic ConversionLysogenic Conversion
The prophage DNA as a gene recombinedThe prophage DNA as a gene recombined
with chromosome of host cell and assign somewith 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)

ConjugationConjugation
Transfer of DNA from a donor to aTransfer 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 acells. In bacteria there are two mating types a
donor (male) and a recipient (female) and thedonor (male) and a recipient (female) and the
directiondirection of transfer of genetic material is oneof transfer of genetic material is one
way; DNA is transferred from a donor to away; 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+
Curing
Integrate
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 Fbecomes F++
while Fwhile F++
remains Fremains F++
• Low transfer of donor chromosomal genesLow transfer of donor chromosomal genes
Physiological States of F FactorPhysiological States of F Factor

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

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 lowHigh 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
Tn9
Tn21
Tn 10
Tn8
RTF
R determinant
 R determinantR determinant
 Resistance genesResistance genes
 TransposonsTransposons

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 implications
Application in diagnosis, treatment andApplication in diagnosis, treatment and
prevention of infectious diseasesprevention of infectious diseases
Eg. L-formEg. L-form
PCRPCR
Detection 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

SummarySummary
1.Phage 2.Transposable elements1.Phage 2.Transposable elements
3.Lytic or virulent phage 4.Lysogenic or temperate phage3.Lytic or virulent phage 4.Lysogenic or temperate phage
5.Transformation 6.Transduction5.Transformation 6.Transduction
7.Conjugation 8.Lysogenic conversion7.Conjugation 8.Lysogenic conversion
9.Protoplast fusion 10.Ames Test9.Protoplast fusion 10.Ames Test
11.11. Briefly describe types of genetic materials in bacteria . Briefly describe types of genetic materials in bacteria .
12.Briefly describe the differences between generalized-transduction12.Briefly describe the differences between generalized-transduction
and specialized (restricted)-transduction.and specialized (restricted)-transduction.
13. Briefly describe the forms of genetic recombination in bacteria.13. Briefly describe the forms of genetic recombination in bacteria.
14.Describe the practical implications of bacterial heredity and14.Describe the practical implications of bacterial heredity and
variations.variations.

3 heredity and variation of bacteria

3 heredity and variation of bacteria

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