Taheri H orizontally T ransferred Genetic Elements and Their Role in Pathogenesis of Bacterial Disease 1 C Gyles and P Boerlin Outline Transfer of foreign DNA Mechanisms of transfer of DNA ID: 220126
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Slide1
Aynaz Taheri
Horizontally Transferred Genetic Elements and Their Role in Pathogenesis of Bacterial Disease
1
C.
Gyles
and P.
BoerlinSlide2
Outline
Transfer of foreign DNAMechanisms of transfer of DNAMobile genetic elements (MGE)MGEs in the virulence of 4 major pathogensConclusion 2Slide3
Transfer of DNA
Foreign DNA originated from another organism and inserted to a bacterium. Characteristics: Different G+C percentage Codon usage Regions that are adjacent with the foreign DNA Horizontal or Lateral Gene Transfer (LGT) Mobile
Genetic Element (MGE) Mechanisms of transfer of DNA
3Slide4
1. Conjugation
Direct cell-to-cell contact
4Slide5
2. Transduction
5
DNA transferred by a virus Slide6
3. Transformation
6
Direct uptake of naked DNA
2
2
2Slide7
MGEs
7ElementsMechanism of Transfer
Plasmid
Conjugation
Bacteriophage
Transduction
Integrative and conjugative elements (ICE)
Conjugation
Pathogenicity island (PAI)
Transduction, Conjugation, Transformation
Insertion Sequences , Transposon
TransformationSlide8
Insertion Sequence (IS)
Small segment of DNA Encode gene for mobilization and insertion.Simplest type of transposable elements found in bacteria.Two characteristics: 700 to 2500 bp, code proteins in transposition
8Slide9
Transposon
Barbara McClintock’s discovery of these jumping genes earned her a Nobel prize in1983 Transposons carry other genes in addition to transposition functionIntrabacterial movement of DNAThey may be transferred to other bacteria by transfer of plasmid or chromosomal DNA9
Interrupted
DNA sequence
Interrupted
DNA sequence
Target site
Target site
Transposon
Transposon
Cut and paste
Copy and pasteSlide10
Plasmid
Small DNA molecule within a cell that is physically separated from a chromosomal DNA Plasmids can perform conjugationPlasmids carry such as genes drug resistance, virulence factors, and fitnessPlasmid encoded many bacterial toxins: Bacillus Anthracis: pathogen of anthrax (PXO1)
Yersinia Pestis: pathogen of plague
10Slide11
Bacteriophage
Bacterial viruses that invade bacterial cells Composed of proteins that encapsulate a DNA or
RNA genome Phages replicate within the bacterium following the
injection
of their genome into its
cytoplasm
Bacterial
toxins
in
the genomes of
phages:
Corynebacterium
diphteriae
Botulism:
b
otulinum
toxin
CTX: cholera toxin
11Slide12
Pathogenicity Island (PAI)
Genomic islands (GEIs) are large segments (10-200 kb) of foreign DNA GEIs are usually flanked by IS and are inserted close to tRNAGEIs that carry virulence genes are called PAIs Mobilization for PAIs: conjugation, transduction and transformation
12Slide13
Integrative and Conjugative element (ICE)
Mobile genetic elements that reside in the host cell’s chromosomeMobilization: conjugationTransfer large amount of genetic materials Common features with transposons, bacteriophages and plasmids:Integrative ability of bacteriophages or transposonsTransfer mechanisms of conjugative plasmids
13Slide14
Virulence of Four Pathogens
Roles of horizontally transferred genes in virulence of bacterial pathogens:E. coliSalmonellaPyogenic SterptococciClostridium
perfringens and Necrotic Entries
14Slide15
E. Coli
Escherichia coli is a rod-shaped bacterium of the genus Escherichia.Core of important genes + accessory genome
Core DNA: ratio of G+C 50.8%, 1700 genesGenome size from 4.6 to 5.6 MbComplexity
of gene
organization by
Insertions, deletions and rearrangement
over time.
15
E. Coli
Nonpathogenic
P
athogenic
E
ncodes
more than 1600 proteins that are not found in nonpathogenic
Plasmids, phages and PAIs transferred to nonpathogenic
Enterotoxigenic E. Coli: diarrhea Slide16
Salmonella
A genus of rod-shaped bacteria of the enterobacteriaceae family. Salmonella bongori
, Salmonella enterica
A pathogen
that can invade intestinal
cells and causes
different enteric and systemic diseases
.
E. Coli and Salmonella have the same
ancestor.
Accessory genome consisting of PAIs,
bacteriophages, and plasmids
.
21 PAIs in Salmonella, called Pathogenicity Islands Salmonella (PIS)
PIS-
1
and
PIS-2
:
Invasion
in
nonphagocytic
cells and
replication
in phagocytic and
nonphagocytic
cells.
16Slide17
Pyogenic Streptococci
An important group of human and animal pathogensRole of MGEs in the virulence and host adaptationStreptococcus pyogenes: human specific pathogen Local pyogenic infections, septicemia, toxic shock syndrome, necrotizing fasciitis and
postinfection rheumatic fever
113 genes acquired by S.
pyogenes through LGT are located in
prophages
,
including 5 virulence
genes.
S
treptococcus
agalactiae
:
main
hosts
are cattle and humans
I
mportant
LGT between S.
agalactiae
and S.
pyogenes
ICEs
in S.
agalactiae
containing virulence genes
and adaptation genes
in cattle
Streptococcus
canis
,
streptococcus
equi
17Slide18
Pyogenic Streptococci
Streptococcus canis: was first isolated in dogs An important pathogen of dogs and also other animal species, including cattle Presence of multiple MGEs in S.
canis involving virulence genes
P
hages, ICE and plasmid
18Slide19
Clostridium perfringens
and Necrotic EnteritisA rod-shaped bacterium of the genus Clostridium. C.Can be found as a normal component of decaying vegetation, marine sediment, the intestinal tract of humans and other vertebrates, insects, and soil. Plasmids have a critical role in diseases: tetanus toxin, enterotoxin
, cytotoxin, NetB toxin
Necrotic
Enterities
: hosted by poultry
Necrotic enteritis has been identified in broilers, laying hens, turkeys and quail
Caused by
toxins
produced by C.
perfringens
MGEs have important role on this economically important disease
19Slide20
Conclusion
Understanding of bacterial adaptability, pathogenesis, and evolutionConduct genome searches for foreign genes that affect adaptation to the animal or human environmentRecognize likely developments in the years aheadFind activities that accelerate the emergence of new virulent pathogens continuously created through LGT
Reduce the capability for treating the disease they cause
20