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Wolbachia – a Heritable
Endosymbiont
Patricia Sidelsky
Symbiosis
Wolbachia
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Classified in a monophyletic
clade in Domain Bacteria

A member of
Alphaproteobacteria –
Related to Rickettsia

Sequencing of 16sRNA
connects Wolbachia to
Ehrlichia and Rickettsia

16srRNA sequences used to
determine relationships
between Rickettsia

Estimated to infect 15-20%
of arthropods. New
estimates include as many
as 50% of insect species

Broad host range – Insects,
isopods, mites, and
arachnids. They have been
isolated from crustaceans.
More recently found in
Nematodes

Manipulate the reproduction
in their hosts in a number of
unusual ways
http://www.bacterialphylogeny.com/ branching_order_al...
Host - Endosymbiont

Wolbachia are found in the
reproductive tissues of their hosts

The bacterial obligatory
endosymbionts are passed
vertically in the cytoplasm of the
eggs of their hosts

The Wolbachia affects sex
determining factors in insects –
affects the sex of the insect
progeny

The host exerts population
control of bacteria
Wolbachia infected ovaries of insect host
Amy Hise, Science

A force in speciation in
arthropods

Viewed as a possibility for the
evolution of insects
Wolbachia and Reproduction

Vertical transmission –
cytoplasmic inheritance

Causes male killing and
sterility in males
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Induces parthenogenesis

Cytoplasmic
incompatability( conflict
between cytoplasmic and
nuclear components)
Insect egg containing Wolbachia
http://www.rochester.edu/.../ images/Wolb_egg.jpg
Symbiont related Sexual
Anomalies

Thelytoky occurs in
Trichogramma wasps

Feminization of males

In wasps there is a
haplofiploid situation with
males haploid and females
diploid.

Occurs in Isopods

Suppresses the androgenic
gland and causes males to
become functional females

Virgin Females produce
diploid females without
fertilization. The n( haploid)
is converted to 2n( diploid)

This occurs early in the first
mitotic division
http://www.biconet.com/flies/FC3.html
http://www.biodiversity.org.uk/.../images/isopods.jpg
Cytoplasmic Incompatability and
vertical transmission

If both male and female
insects are infected with
Wolbachia – the progeny will
be infected

If the female is infected and
the male is not infected, the
progeny will all be infected.

If the female is not infected
and the male is infected
there will not be any progeny
http://www.cdc.gov/ncidod/eid/vol4no4/beard6t.gif
Examples of symbiont – host interactions
Adalia bipunctata – http :bugguide.net/ node/view/13976
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Acraea encedon- www2.nrm.se/.../e/
acraea_encedonfumosa.html
Male killing mechanism has been studied in two species of insect
In Adalia bipunctata and Acraea encedon the presence of Wolbachia
halves the hatch size and changes the female/male ratio
Microbial nature of infection has been verified by treatment with rifampin
and sulphamethoxazole
After treatment with antibiotics the hatch size returns to normal and the
with a normal sex ratio
Condition can be artificially induced by injection of macerated infected
insect into pupae of uninfected ( Hurst et al)
Why Male Killing ?

Reduces competition for food ( H)

Reduces cannibalism in siblings (H)

Improves female fitness for breeding- selective advantage
(H)

Insures propagation of Wolbachia endosymbionts to future
generations ( S + H)
H= Host selective advantage S= Symbiont selective advantage
Mechanism of Action

Bacterial modification of
sperm by bacterial
interactions

Bacteria present in testes
interact with DNA binding
proteins – These
may be similar to H1,
histones

The same bacterial strain
must be present in the
female in order to rescue the
egg
HI – Protein database

Mitotic defects appear in the
early divisions of the
fertilized egg( during
cleavage)
Wolbachia – Evidence for specificity of infection

PCR for 16sRNA from infected
lines
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Product purified and ligated
into pGEM vector
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Plasmids were transformed
into DH5a
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Colonies with insert were
detected
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39 /42 positive for Wolbachia
insert and not other bacteria
16sRNA
Transformants are recognized by blue
color on agar plate
Wolbachia and genetics

Genome recently sequenced

Loss of genes due to obligatory
nature of relationship between
bacteria and host

Loss of genes over time due to
dependency on host

Many repetitive elements and
insertion sequences in the
genome

Imply high level of intergenomic
and intragenomic recombination
Genomic map of Wolbachia
NCBI
http://www.ncbi.nlm.nih.gov
Genetics of Wolbachia
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Wolbachian genome consists of one
circular chromosome

1.26Mbp – 1195 proteins – GC
content 35%

Contains genes with
Ankyrin repeats – Ankyrins connect
endosymbionts to the cell cytoskleton
which is an adaptation for intracellular
existence

Type Four Secretion System –
required for persistence of
endosymbiont in host – conserved in
Rickettsia
Female Drosophila melanogaster – laying egg
P. Sidelsky – Motic Camera
Lateral Transfer of Genes

Evidence of lateral( horizontal)
transfer of genes in Wolbachia
species in Drosophila
melanogaster and Nasonia
vitripennis.

Drosophila and Nasonia can
maintain infection by two strains
of Wolbachia

Exchange between bacteria that
coinfect in the same cells
( density dependent)
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Exchange between
endosymbiont and host( gene
loss)

IS sequences in Wolbachia
suggest Bacteriophage transfer
between Wolbachia strains.

Recent research has detected 3
prophage sequences in the
Wolbachia genome.
( Wu et al)
Importance of study

Wolbachia does not infect
humans – studying Wolbachia
can lead to a better
understanding of Rickettsial –
host interactions for medical
applciations

Understanding Wolbachia can
lead to vector control in
infections such as Rocky
Mountain Spotted Fever
( Rickettsia and tic)

Since Wolbachia infects diverse
species of insects including
beetles, fruit flies, and
mosquitoes, it could be
evaluated for a form of biological
control

Used as a model to study
speciation
Mediterranean Fruit Fly
http://creatures.ifas.ufl.edu/fruit/mediterranean_fruit_fly
.htm
Wolbachia and River Blindness

Wolbachia has also been identified in
filarial worms
( Nematoda)
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One of these worms causes
Riverblindness(Onchoceriasis)
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Wolbachia provides metabolic
support through many pathways
for the worm.
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Contributes to inflammatory
responses
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Instead of antihelminth drug protocols
– will antibiotics be a cure??????
http://tools.neb.com/wolbachia/
References
Anderson,Cort and Timothy Karr. Wolbachia:Evolutionary Novelty in a Rickettsial
Bacteria. BMC Evolutionary Biology, 2001:1-10.
Huigens,M.E. On the Evolution of Wolbachia Induced Parthenogenesis in
Trichogramma Wasps.
http://www.gcw.nl/dissertations/3389/dis3389.pdf
Hurst, Gregory et al. Male-Killing Wolbachia in Two Species of Insect.
National Center for Biotechnology Information – ncbi. http://www.ncbi.nlm.nih.gov/
Johanowicz,Denise et Marjorie Foy.Wolbachia Endosymbionts. Florida
Entomologist.1998: 310-316.
Protein Data Bank - http://www.rcsb.org/pdb/
Rigaud, T., Juchault, P., and Mocquard, J. P. 1991. Experimental study of the sex ratio
of broods in terrestrial Crustacea Armadillium vulgare. Possible implications in
natural populations. J. Evol. Biol. 1991: 603 - 607.
Sun,Ling. Et al. Gene Organization in the dnaA Region of Wolbachia. Jornal of
Bacterioology. 199.18115):4708-4710.
References( con)
Wernegreen,Jennifer Endosymbiosis: Lessons in Conflict Resolution. Plos
Biology. March 2004, 2:307-311.
Werren,John H. Biology of Wolbachia. Annual Review of Entomology.
1997.42:587-609.
Werren, John H. and Leo Beukboom. Sex Determination, Sex Ratios, and
Genetic Conflict.Annual Review of Ecological Systematics. 1998,29:233261.
Werren, John H. and David Windsor. Wolbachia Infection Frequencies in
Insects: Evidence of a Global Equilibrium. Proceedings of the Royal
Society. 200 267: 1277-1285
Werren, John H. Wolbachia Run Amok. Proceedings of the National
Academy of Science. 1997. 92: 11154-11155
Wu,Martin et al. Phylogenomics of the Reproductive Parasite Wolbachia
pipientis wMeI: A Streamlined Genome Overrun by Mobile Genetic
Elements. Plos Biology. 2004,2:327-333.