Microbial diversity of soil

Soil is an ecological niche contains all major groups of microorganism - bacteria, fungi, algae, protozoa and virus, but bacteria are most numerouse each play a vital role in the ecological diversity.

1. MICROBIAL DIVERSITY
OF SOIL

2. MICROBIAL DIVERSITY
OF SOIL
Soil contains all major groups of
microorganisms-bacteria, fungi, algae,
protozoa, and virus, but bacteria are the
most numerous .
Usually the topsoil contains the greatest
number of microorganisms due to the
sufficient supply of oxygen and nutrients.

3. Compared with topsoil, the lower layers of
soil contains fewer microorganisms due to
the depletion of oxygen and nutrients.
It generally believed that there are many
microbial species in soil, which are yet to
be discovered.
70%
14%
13%
3%0%
Anerobic bacteriaAnaerobic bacteria
Actinomycetes Fungi
Other organisms

4. BACTERIA
The bacterial population of the soil exceeds
the population of all other microbial groups in
both number and variety.
The soil-borne bacteria are autotrophsand
heterotrophs; mesophiles, thermophiles, and
psychrophiles; aerobes and anaerobes;
nitrogen fixers, nitrifying and denitrifying;
cellulose, protein, pectin and urea digesters;
and many other kinds of bacteria.

5. Typical bacillus, and pseudomonas are most
commonly isolated soil bacteria.
Bacillusspecies represent 7-67% of soil
isolates, have diverse metabolism , survive
a pH range from 2 to 8 and temperature
range from -5% to 75% .
Pseudomonasspecies represent 3-15% soil
isolates, are noted for their diverse
metabolism, particularly their ability to
degrade organic chemicals like pesticides.

6. EXAMPLE

7. On the soil surface few cyanobacteria
would be present, which carry
photosynthesis. The cyanobacteriaplay a
key role in the transformation of rock to
soil, a first step in rock -plant succession.

8. EXAMPLE

9. The filamentous bacteria (Actinomycetes)
are important soil components, especially
under high pH, high temperature and water
stress, their number is generally smaller
then the typical bacteria.
They have an unique ability to degrade
chitin, cellulose, hemicelluloses and other
complex organic substance found in the
soil. Therefore, they play an important role
in building soil fertility.

10. The Actinomycetesare also noted for their
ability to synthesis and excrete antibiotics
which give them a competitive advantage in
the soil. Some of the important Actinomycete
genera found in the soil are Streptomyces,
Actinoplanes, Nocardia,
Agromyces, Arthrobacter, Micromonospora,
Microbispora, and Streptosporangium.

11. EXAMPLE

12. FUNGI
Most of the soils are inhabited by different
species of fungi. They exist in both the
mycelialand spore stage and are abundant
in topsoil, the aerobic surface layer of the
soil.
Their numbers range from 10
5
to 10
6
/ g of
soil. However, despite their low number in
comparison to bacteria, fungi, usually
contribute a higher proportion of the total
soil microbial biomass. This is due to their
relative large size (hyphae2-10um width).

13. Some fungi , primarily yeasts, can survive in
anaerobic environments by fermenting
sugars into alcohol.
The yeast are less numerous (up to 10
3
/g
soil) than aerobic mycelialfungi.
fungi are important in the development of soil
structure, which is crumble structure, that is
entangling of the fine soil particles by the
mycelium to form water-stable aggregates.

14. They are very important components of the
soil with respect to nutrient cycling and
decomposition of major constituents of plant
tissue, namely cellulose, hemicellulose,
starch , lignin, and pectin.
Cellulose decomposing fungi include
Ascomycetesand Deuteromycetes, such as
Aspergillus, Penicillium, Chaetomium,
Trichoderma,Fusarium,Stachybotrys,
Memmoniella,Humicola,Phoma,
Cladosporium,Alternaria,Acremonium,
Myrothecium,Thielaviaetc.

15. They produce cellulases, which are involved in
the breakdown of cellulose into simple sugars.
Degradation of hemicelluloseis accomplished
by a number of fungal species belonging to
Alternaria, Aspergillus, Chaetomium, Fusarium,
Glomerella, Penicillium, and Trichoderma.

16. Similarly , pecticsubstance, the primary
constituents of the middle lamella, and
primary cell wall are broken down fungal
pectinasesproduced chiefly by Rhizopus,
Aspergillus, Penicillium, Monilia,
Fusarium, Geotrichumand Rhizoctonia
species.
Lignin, the chief constituent of woody parts is
broken down by white rot fungi
(Basidiomycetes) , such as Phanaerochaete
Chrysosporium.

17. EXAMPLE

18. ALGAE
The population of algae in soil is less
numerous than that of either bacteria or
fungi but is more numerous than protozoa.
The major types present are green algae,
diatoms and yellow-green algae. Algal
colony forming units vary between 10
3
-10
6
per gram of soil. algal populations vary,
depending on soil type.

19. For example , in temperate soils, green
algae are more numerous than diatoms,
which in turn are more numerous than
yellow-green algae. green algae dominate
in acid soils, whereas diatoms grow best in
neutral soils.

20. EXAMPLE

21. On account of their photosynthetic nature,
algae are found in the upper layers of soil
where there is both water and light. In a
fertile soil, the biochemical activities of
algae are dwarfed by those of bacteria and
fungi. But, in some conditions, algae
perform beneficial changes and are thus
prominent in such situations.

22. For example , on barren and eroded lands,
they may initiate the accumulation of organic
matter because of their photosynthetic and
other metabolic activity. Such a condition is
also observed in some desert soils and is
known to pave a way for the growth of other
microorganisms.

23. Environmental factors exert a control on
the algal population of soil. Temperature is
one of the controlling factor as the algae
usually become less active in winter.
Water is also a controlling factor as algal
blooms are often observed after rainfall.

24. Algae , can adapt to soil environment with
high salt content by pumping sodium ions
(Na
+
) out of the cell and pumping
potassium(k
+
) into the cell. The potassium
ions are much less damaging to the algae,
and by providing osmotic balance, they help
the algal cells from losing water to their
salting environment.

25. Soil fertility has also a direct effect on the
abundance of algae. Since algae produce
their own carbohydrates , it is due the lack
of soil nutrients , such as N, P and K, that
help to control algal growth. Herbicides also
reduce algal populations of the environment.

26. PROTOZOA
They are unicellular eukaryotic microorganism
found mainly in the top 15-20 cm of the soil.
Total protozoa may range from 1,00,000 to
3,00,000 per gram of the upper soil surface ,
though a typically range would be 10,000-
1,00,000.
Protozoa of each of three major groups, the
flagellates, amoebae, and the ciliates, are
found in soil environment .But flagellates are
the most numerous of the protozoa in a
typically soil and they dominate acid soils.

27. Protozoa have a limited role in affecting
soil environmental conditions such as
structure and pH.However, they affect the
structure and function of microbial
communities because they are predatory.
They play an important ecological role in
regulating bacterial populations in soil.
Eliminating protozoa from the soil
decreases the overall decomposition rate
of organic matter in soil. This suggests
that protozoa help to stimulate
decomposition.

28. EXAMPLE

29. VIRUSES
Human and animal viruses periodically find
their way into soils through addition of
wastes. These viruses are an environmental
concern when they survive in soil and move
into the water table. Plant viruses rarely
survive in soil, but some insect viruses
remain infective for years. Many soil
microorganisms themselves may harbor
viruses require transmission by nematodes
or fungi.