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Bacteria Missing Falgella
Name: Hussam
Status: Student
Age: 20s
Location: N/A
Country: N/A
Date: October 2002
Question:
When some bacteria are grown in lab conditions, they
fail to develop flagella. Why is that the case?
Replies:
Dear Hussam:
I do not know the exact bacteria that you're describing, but I would think
that they might not produce flagella because their nutrient supply is
readily available in culture. In nature, the primary function of the
flagella is to drive the bacteria toward food sources. This ability would
not be necessary under typical culture conditions, so the bacteria might
be able to conserve energy by not producing flagella.
Thanks for the good question,
Jeff Buzby, Ph.D.
Children's Hospital of Orange County
When bacteria have the ability to switch off the production of outer
structures such as flagella or
fimbriae (pili) this is called 'phase variation'. The mechanisms behind
this variation are various, but
usually they are caused by mutations, often a single nucleotide change, or
small deletion/insertion, or a reversible fragment of DNA (a flip-flop)
during replication. Most of these mutations are reversible, for instance,
a reversible fragment can reverse back to the 'expression on' direction. A
single nt mutation can reverse back, which is frequently the case in
nucleotide stretches like GGGGGGG (the number of nucleotides can change at
high frequency in such
stretches).
Such mutation hot spots are frequently found in the genes encoding the
structural components of flagella or fimbriae, or in their regulatory
genes. The result is an on-off switch at frequency higher than normal
mutation rates (say, 1 in every 100 or 1000 generations, rather than 1 in
a million).
This can be observed in the lab, since the mutation results in a visible
colony morphylogy change. It is proposed that the same thing happens in
nature, and that bacteria lacking such structures are at a disadvantage
when colonizing a host. They may be at an advantage when surviving outside
the body, though, and since the process is reversible one can see
fluctuations in a bacterial populations with or without expression of such
structures.
In addition, certain bacteria have outer structures whose expression is
tightly regulated by external factors such as temperature. The fimbriae of
E. coli are such an example, and by growth at certain temperatures they
can either produce fimbriae or not.
Trudy Wassenaar
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Update: June 2012
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