An example of how structures on the surface of bacteria change due to the genes controlling them

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An example of how structures on the surface of
bacteria change due to the genes controlling them
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Many different structures protrude from the
surface of the bacteria
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This is a model representing a structure
(lipopolysaccharide or LPS) that is on the
surface of the bug, that we are using to make a
vaccine
This surface structure is made up of separate
sugar units
The different colours on the model show the
different sugars
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Each sugar unit is added by the product of a
single gene
Each gene product adds a specific sugar at a
specific position
e.g. The purple sugar can only be added to the
blue sugar
Four of these genes can be switched on and off
by a mechanism called phase variation
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If this structure is further simplified so that
each different sugar is represented by a shape,
it looks like this
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The genes lgtA and lgtB can be switched on and
off
The genes lgtA and lgtB both need to be on to
get this large, fully extended structure
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then the blue sugar is not added and so the
purple sugar can not be added either
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then the turquoise sugar is not added
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the blue sugar can not be added because the
turquoise sugar is missing
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This mechanism of switching genes on and off,
causes a change in the structure
This example was in just one of many surface
exposed structures on the bacteria
This switching on and off occurs in many of
these other structures
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This means there are many different surface
structures
This mechanism has evolved so that bacteria can
constantly change and evade the bodies immune
response
We are using part of the LPS structure which is
always present, whichever genes are switched on
and off to make a vaccine against this bacterium