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Bacteria Classification
Name: Anisah O.
Status: Other
Age: 30s
Location: N/A
Country: N/A
Date: N/A
Question:
Except for the shape, are there other
ways by which different bacteria can be classified?
Replies:
Morphology, that is the shape of bacteria, is still an
important tool for the identification of species.
Morphology in combination with specific staining
procedures (Gram stain for example) is routinely used
for identification. However that is not sufficient for
classification: definingh which species are related.
Modern classification of bacteria is heavily dependent
on the DNA sequence of a particular component of their
ribosomes. Ribosomes are the particles that produce
protein from RNA. They consist of protein and RNA
themselves, and their RNA is strongly conserved
between species. Since they evolve slower than other
genes they are used as a tool to group bacteria
together that are believed to have evolved from a
common ancester. Their ribosomal RNA would be very
similar. The sequence of this socalled 16S RNA is used
to generate phylogenetic trees. These should represent
the evolution of related species from common
ancesters.
Other than this, rather fancy, genetic tool, bacteria
are classified according to their total DNA content,
which can have more G+C than A+T, or the other way
round. The G+C content is relatively conserved between
related species. This is combined with biochemical
properties and growth characteristics. The latter is
often used to subdivide related bacteria into species
or sub-species. They can be measured by growing
bacteria on specific media, or by performing specific
biochemical reactions on them. That is the classical
bacteriology that is routinely performed in
bacteriological laboratories.
Frequently, bacteria are isolated that do not fit in
the schemes of species that we have. Novel species are
frequently discovered. Less frequently, novel genera
are described. These are usually not newly discovered
bacteria (the discovery of a completely novel genus is
the exception), but rather existing genera and species
that, on the basis of their ribosomal RNA or other
characteristics, are now believed to belong to a
different genus than they were ascribed to. The result
is that they get a new name, and this renaming (as a
consequence of reclassification) of bacteria can be
quite confusing.
Trudy Wassenaar
In addition to individual shape bacteria can be classified by:
1. colony shape in culture
2. motility
3. morphological characteristics other than shape...eg multiple flagella
4. metabolic activity...eg. What sugars do they ferment
5. and DNA sequence
Peter Faletra Ph.D.
Office of Science
Department of Energy
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Update: June 2012
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