Pseudomonas syringae
What are they?
Pseudomonas syringae
bacteria can infect a
wide range of plants
including: apple, bean,
pea, beetroot, stone
fruit, barley, wheat and
horse chestnut trees.
How do they infect?
Pseudomonas syringae bacteria infect
plants through natural openings, such as
plant breathing holes called stomata in
leaves and lenticels in woody tissues.
The bacteria produce toxic chemicals
that modify surrounding plant cells,
allowing bacteria to infect and multiply.
One toxin called coronatine forces the
plant to keep its stomata open so that
bacteria can then enter through them.
What do they look like?
Rod shape
The bacteria are rod-shaped, which
allows them to ‘squeeze’ into plant cells
through plant wounds.
Swimming tails
The bacteria have flagella, which are
whip-like protein tails that help the
bacteria swim through the soil and
towards plants. The bacteria can also
use their flagella to swim aound on the
plant surface – they are the cheetahs of
the microbial world!
What happens next?
Once the bacteria enter the plant, they
thrive in the space between cells where
they feed on plant nutrients.
Instead of breaking down plant cell walls,
the bacteria inject proteins into plant
cells. These proteins can prevent the
plant from detecting bacteria, remodel
plant cell functions and promote
bacteria growth.
Symptoms
The bacteria cause
ugly blisters to form
on fruit. They can also
cause cankers to form
on trees. Cankers girdle
and squeeze tree trunks, cutting off the
nutrient and water supply to branches
and fruit. The bacteria can eventually kill
trees!
Ice weapons!
Some Pseudomonas syringae bacteria
have ice-making proteins on their
surface that help to form ice crystals.
These ice crystals grow and pierce plant
cells creating more wounds, through
which the bacteria can enter the plant.
Why are P. syringae
bacteria important?
These bacteria can infect a huge range
of plants and are a major threat to
woody plants. The strain Pseudomonas
syringae pv. aesculi causes bleeding
canker in horse chestnut trees. This is
when the infected bark
is orange and brown
with oozing sticky liquid
coming out from the
wound. Around a half of
UK horse chestnut trees
are now affected by this
disease.
How do they spread?
Pseudomonas syringae bacteria are
spread by rain, and insects feeding on
infected plants. They can also be spread
by planting infected material or using
contaminated pruning tools. Spread of
disease is favoured by wet conditions
and temperatures of 12 – 25°C.
What can be done to
stop them?
Growing resistant plants that are better
able to defend themselves from attack.
It’s also possible to use “fruit yeasts”
which are fungi that occur naturally in
fruit and are adapted to fight off these
bacteria.
Did you know?
The ability of Pseudomonas syringae to
create ice crystals has led scientists to
investigate these properties for artificial
snow production on ski slopes!
Questions
1. Which human disease does
Pseudomonas syringae remind you of?
2. Why do the bacteria target stomata?
3. How do the bacteria enter plants?
4. Why is it important for farmers to
control the spread of Pseudomonas
syringae?
5. What other living things have a
swimming tail?
Images
1. Image of Pseudomonas syringae by Robert Jackson,
University of Reading
2. Image of Tomato speck disease: Chris Smart, NYSAES,
Geneva NY, Wikipedia.
3. Diagram of Pseudomonas syringae by I. Livingstone.
Copyright Biodidac.
4. Image of ice crystals: Steffan Enbom, Wikipedia
5. Image of horse chestnut bleeding canker disease: Lamiot,
Wikipedia
6. Image of yeast: Masur, Wikipedia.
7. Image of skiing: The Musk, Wikipedia.
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Contact
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[email protected].