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Distribution
of
Micro
Organisms |
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Distribution
of
Microorganisms - The environment may be looked upon as a vast depository of microbes interacting with the environment, with each other and with higher plants and animals. We would briefly examine the three specific environments for microbial cells and populations in particular.
[I] Atmosphere:
This
is
the
simplest,
as
it
is
relatively
uniform
and
constant
in
composition.
There
is
lack
of
nutrients,
water
etc.,
thus
its
major
role
for
microbes
is
as
a
medium
for
dispersal.
There
is
decrease
in
number
of
microbes
with
increasing
altitude.
Most
are
present
as
spores
(mostly
fungal).
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Microbiology
of
the
atmosphere
has
the
following
three
main
applications
for
man.
(1)
In
hospitals,
bed
making
and
floor
sweeping
may
create
aerosols
of
pathogens,
giving
rise
to
variation
in
size
and
species
composition
of
the
airborne
population.
(2)
germ
warfare,
where
the
aim
is
to
maximize
spore
viability
and
infectivity,
and
to
control
when
and
where
the
cells
come
to
the
ground.
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(3)
spread
of
plant
pathogens,
most
being
fungal
spores.
In
all
the
above
cases
it
is
important
to
know
the
mechanisms
creating
aerosols,
factors
which
cause
them
to
settle,
and
duration
periods
over
which
airborne
organisms
remain
viable
and
infective.
[II] Aquatic
environments:
These
are
the
major
site
for
microbial
growth,
with
more
than
70%
of
the
earth's
surface
covered
by
oceans.
Growth
is
generally
slow,
because
of
low
temperature
(90%
of
the
world's
sea
water
is
always
below
4°C)
and
low
concentrations
of
organic
matter.
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The oceans contain 0.4-10 mg organic carbon/ml, suspended microbes, 10-l000/mI. Microbes are said to be oligotrophic. Photosynthetic forms are stratified according to their wavelength requirements. Some minerals, particularly nitrate, phosphate and sulphate often limit the growth of algae in water. Various factors cause an increased addition of such nutrients to inland waters.
This process of enrichment is called eutrophication and it may be caused by sewage, industrial waste or by drainage from agricultural land which is being intensively farmed. Due to eutrophication, there develop algal blooms.
[III] Soil:
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Soil represents the most varied and heterogeneous environment for microbes. It has solid, liquid as well as gaseous phases. The solid phase has complexes of day minerals and organic matter.
The remaining volume (pore space) is filled with water (containing soluble organic and inorganic material), and the soil atmosphere, which is saturated with water, with less 02 and more CO2 than the atmosphere above the soil.
The environment of a microbial cell in soil is in fact a microhabitat, where conditions may be much different from those in the bulk soil. For instance a cell growing on a piece of decaying root in soil, may have an excess of carbon and nitrogen while the soil as a whole may be nutrient deficient. Different conditions may prevail in microhabitats.
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For example, aerobes may grow on the outside of soil crumb or microbial film whereas anaerobic processes occur in the centre.
The number of microbes decreases with soil depth. About 1gram of garden soil will contain 107 bacteria and 5 meters of fungal hyphae.
About 1 hectare of typical agricultural field contains almost 6,000 kg wet weight of microbial biomass, which is the weight of 80 sheep. Most soil activity comes from enzymes, as ureases, phosphatases and dehydrogenases. They are important in degradation.
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