Microbiology
is
the
study
of
microorganisms,
including
unicellular
(single-celled)
eukaryotes
and
prokaryotes,
fungi,
and
viruseses.
Today,
most
of
the
work
in
microbiology
is
done
using
methods
from
biochemistry
and
genetics.
It
is
also
related
to
pathology,
as
many
microorganisms
are
pathogens.
Microbiologists
have
made
many
fundamental
contributions
to
biology,
especially
in
the
fields
of
biochemistry,
genetics,
and
cell
biology.
Microbes
have
many
traits
that
make
them
ideal
model
organisms:
They
are
small,
therefore
they
do
not
consume
many
resources
Some
have
very
short
generation
times
(~30
minutes
for
E.
coli)
Cells
can
easily
survive
in
isolation
from
other
cells
They
can
reproduce
by
mitotic
division,
allowing
for
the
propagation
of
genetically
identical
(clonal)
populations.
They
may
be
frozen
for
long
periods
of
time.
Even
if
90%
of
the
cells
are
killed
by
the
freezing
process,
there
are
millions
of
cells
in
a
milliliter
of
liquid
culture.
These
traits
allowed
Joshua
and
Esther
Lederberg
to
devise
an
elegant
experiment
in
1951
demonstrating
that
adaptive
mutations
arise
from
preadaptation
rather
than
directed
mutation.
For
this
purpose,
they
invented
replica
plating,
which
allowed
them
to
transfer
numerous
bacterial
colonies
from
their
specific
locations
on
one
agar-filled
petri
dish
to
analogous
locations
on
several
other
petri
dishes.
After
replicating
a
plate
of
E.
coli,
they
exposed
each
of
the
new
plates
to
phage.
They
observed
that
phage-resistant
colonies
were
present
at
analogous
locations
on
each
of
the
plates,
allowing
them
to
conclude
that
the
phage
resistance
trait
had
existed
in
the
original
colony,
which
had
never
been
exposed
to
phage,
instead
of
arising
after
the
bacteria
had
been
exposed
to
the
virus.
The
extensive
characterization
of
microbes
has
allowed
them
to
be
used
as
tools
in
other
branches
of
biology:
Bacteria
(especially
E.
coli)
may
be
used
to
replicate
DNA
in
the
form
of
a
plasmid.
This
DNA
is
often
chemically
modified
in
vitro
then
inserted
into
bacteria
to
select
for
the
desired
traits
and
isolate
the
desired
product
from
by-products
of
the
reaction.
After
growing
the
bacteria
and
thereby
replicating
the
DNA,
the
DNA
may
be
further
modified
and
inserted
into
other
organisms.
Bacteria
may
be
used
to
produce
large
amounts
of
protein
using
genes
encoded
on
a
plasmid
Bacterial
genes
have
been
inserted
into
other
organisms
as
reporter
genes.
The
yeast
two-hybrid
system
combines
bacterial
genes
with
genes
from
the
organism
being
studied
and
inserts
them
into
yeast
cells
to
study
protein-protein
interactions
within
a
cellular
environment.
