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Gram
Negative
Aerobic
Rod
and
Cocci |
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This
part
comprises
of
bacteria
belonging
to
a
large
number
of
taxonomic
groups,
differing
in
morphology,
physiology
and
metabolic,
processes
and
includes
five
important
families
such
as
the
Pseudomonadaceae,
Azotobacteraceae,
Rhizobiaceae,
Methylomonadaceae
and
Halobacteriaceae.
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The
family
Pseudomonadaceae
includes
bacteria
which
are
straight
or
curved
rods
and
are
motile
by
polar
flagella.
These
bacteria
are
a
versatile
group
of
chemoorganotrophs
and
have
an
oxidative
metabolism.
G
+C
content
ranges
between
58-70
moles
percent.
This
family
includes
organisms
that
can
grow
in
mineral
media
with
a
single
organic
compound
as
sole
source
of
carbon
and
energy.
Most
pseudomonads
are
common
inhabitants
of
soil,
freshwater
and
marine
environment.
A
few
are
pathogenic
to
plants
and
some,
occasionally
are
animal
pathogens
(P.
aeruginosa).
Some
Pseudomonas
produce
bacteriocins
called
pyocins.
Type
genus
is
Pseudomonas
which
is
represented
by
a
large
number
of
species
(about
265).
The
genus
Xanthomonas
includes
species
which
are
plant
pathogens.
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The
family
Azotobacteraceae
is
characterized
by
large
cells
which
are
predominantly
rod
shaped
to
oval
and
motile
by
peritrichous
or
polar
flagella
.
The
bacteria
are
heterotrophic
and
capable
of
fixing
molecular
nitrogen
in
a
nitrogen
free
or
nitrogen
poor
medium
with
organic
compounds
as
energy
source.
They
are
strict
aerobes
and
are
inhabitants
of
soil,
water
and
leaf
surfaces.
The
family
includes
four
genera
such
as
Azotobacter,
Azomonas,
Beijerinckia,
and
Derxia
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The
family
Rhizobiaceae
consists
of
bacteria
which
are
rod
shaped,
motile
with
one
polar
or
subpolar
flagellum
or
2.6
peritrichous
flagella.
The
family
has
two
genera
such
as
Rhizobium
and
Agrobacterium.
Rhizobium
species
form
nodules
on
roots
of
legume
plants
and
fix
nitrogen
within
the
root
nodules,
while
species
of
Agrobacterium
do
not
produce
nodules
but
cause
other
types
of
hypertrophy
on
many
plants
and
do
not
fix
atmospheric
nitrogen.
Genus
Rhizobium
is
divided
into
two
sub
groups
based
on
flagellation
and
rate
of
growth on
yeast
extract
media
.
The
species
are
defined
by
the
host
that
they
infect
and
nodulate
.
DNA
base
composition
is
59-65
mole
per
cent.
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The
family
Methylomondaceae
is
represented
by
bacteria
utilising
one
carbon
compounds
such
as
methane
or
methanol
as
carbon
source
and
are
unique
in
their
limited
nutritional
versatility.
It
includes
two
genera
Methylomonas
and
Methylococcus.
The
former
have
a
G
+
C
content
of
52.1
moles
per
cent
while
the
latter
have
62.5
moles
per
cent.
The
family
Halobacteriaceae
is
represented
by
bacteria
which
are
rods
and
cocci
that
need
a
high
concentration
of
NaCL
(2M)
for
growth.
A
major
characteristic
of
this
group
is
that
cell
walls
do
not
contain
diaminopimelic
acid
and
muramic
acid
but
contain
largely
lipoprotein.
Metabolism
is
respiratory
and
little
is
known
about
the
utilization
of
carbohydrates.
Colonies
are
of
various
shades
of
red,
pink,
orange,
vermilion
etc.
The
family
contains
two
genera
namely
Dalobacterium
and
Halococeus.
The
former
is
pleomorphic,
specially
in
deficient
media,
aerobic,
motile
by
a
tuft
of
polar
flagella
or
nonmotile.
Do
not
form
dormant
structures
but
survive
in
salt
solutions
for
many
years.
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The
genus
Haloeoccus
consists
of
bacteria
which
are
cocci,
0.6-1.5 µm
in
diameter
and
occur
in
pairs,
tetrads
and
irregular
clusters
of
tetrads.
They
are
non-motile,
aerobic
and
grow
only
in
the
presence
of
2.5
M
or
higher
concentration
of
NaCl.Among
the
genera
of
uncertain
affiliation,
Acetobacter
and
Brucella
are
important.
The
genus
Acetobacter
has
cells
which
are
ellipsoidal
to
rod
shaped,
straight
or
slightly
curved,
may
be
motile
by
peritrichous
flagella
or
non
motile.
Metabolism
is
respiratory
and
oxidize
ethanol
to
acetic
acid.
Generally,
no
pigments
are
produced.
Found
on
fruits
and
vegetables,
vinegar
and
cause
spoilage
of
alcoholic
beverages.
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