Soil microbiology is the study of microorganisms in soil such as bacteria, actinomycetes, fungi, algae and protozoa. These microorganisms are important because they affect soil structure and fertility through organic matter decomposition, nutrient transformations, and symbiotic relationships with plants. The four major groups of microbes found in soil are bacteria, actinomycetes, fungi, and algae, each playing an important role in soil health and plant growth.

1. SOIL
MICROBIOLOGY
POOJA S NATHAN
S3 BT 44

2. SOIL MICROBIOLOGY
• Soil microbiology is the study of
organisms in soil, their functions,
and how they affect soil properties.
• Microorganisms in soil are important
because they affect soil structure
and fertility.
• Soil microorganisms can be
classified as bacteria,
actinomycetes,fungi,
algae and protozoa

3. SOIL SAMPLE UNDER MICROSCOPE

4. MICROBIAL DISTRIBUTION IN SOIL
Earthworms
12%
other macro
fauna
5%
Bacteria and
Actinomycete
s
40%
Other micro
flaura(eg:fung
i and algae)
40%
Mesofauna
3%

5. 1.BACTERIA

6. • Bacteria and Archaea are the
smallest organisms in soil apart
from viruses.
• Bacteria and Archaea
are prokaryotic. All of the other
microorganisms are eukaryotic.
• Most soil bacteria live close to plant
roots and are often referred to as
rhizobacteria(lives on rhizosphere)

7. RHIZOSPHERE
• 1/10 inch.
• Exudates: carbohydrates
and proteins secreted by
roots.
• Attracts bacteria, fungi,
nematodes, protozoa.

8. Rhizosphere

9. EXAMPLES: :
Some genera like
• Pseudomonas,
• Arthrobacter,
• Clostridium,
• Achromobacter,
• Sarcina,
• Enterobacter etc.

10. PICS:

11. 2.ACTINOMYCETES

12. • Actinomycetes are a fungi-like
bacteria forming long filaments that
stretch through the soil.
• Actinomycetes live predominantly
aerobically and are heterotrophs.
• They have sometimes been
classed as fungi because they
both look like, and decompose
similar material as fungi.

13. • Antibacterial agents work against
them but antifungal agents do not.
• Make “earthy” smell by producing
geosmin
• Adaptable to drought
• Can act in high pH
• Break down “recalcitrant”
compounds

14. • One of the most notable
characteristics of the
Actinomycetes is their ability to
produce antibiotics ,like
Streptomycin

15. EXAMPLES:
• Nocardia asteroides
• Dermatophilus congolensis
• Streptomyces etc.

16. PICS:

17. 3.FUNGI

18. • Fungi are important in the soil as
food sources for other, larger
organisms, pathogens, beneficial
symbiotic relationships with plants or
other organisms and soil health.
• Most of the environmental factors
that influence the growth and
distribution of bacteria and
Actinomycetes also influence fungi.

19. • The quality as well as quantity of
organic matter in the soil has a direct
correlation to the growth of fungi,
because most fungi consume organic
matter for nutrition.
• Fungi thrive in acidic environments,
while bacteria and Actinomycetes
cannot survive in acid.

20. EXAMPLES:
1.Saprophytic fungi (decomposers)
– Pleurotus ostreatus (oyster mushroom)
– Lentinula edodes (shiitake)
– Stropharia rugosoannulata (king
Stropharia).
2. Mutualists Fungi
– Zygomycota
– Basidiomycota

21. 3.Pathogenic fungi
– Pythium,
–Rhizoctonia,
–Phytophthora
–Verticillium.

22. PICS:

23. 4.ALGAE

24. • Filamentous, colonial, unicellular
• Photosynthetic
• Algae can be split up into three main
groups:
– Cyanophyceae
– Chlorophyceae
– Bacillariaceae
• Blue-green algae(Cyanophyceae)
are responsible for nitrogen fixation.

25. EXAMPLES:
• Cyanophyta (Blue-green algae)
• Chlorophyta (Grass-green algae)
• Xanthophyta (Yellow-green algae)
• Bacillariophyta (diatoms or golden-
brown algae)

26. PICS:

27. 5.PROTOZOA

28. • Protozoa are eukaryotic
organisms
• The first microorganisms to
reproduce sexually, a significant
evolutionary step from
duplication of spores, like those
that many other soil
microorganisms depend on.

29. • Protozoa can be split up into
three categories
–Flagellates
–Amoebae
–Ciliates.

30. EXAMPLES:
• Flagellates
–(e.g., Giardia lamblia)
• Amoeboids
–(e.g., Entamoeba histolytica)
• Sporozoans
–(e.g., Plasmodium knowlesi)

31. PICS:

32. IMPORTANCE OF SOIL MICROBES
• Organic matter decomposition
and soil aggregation;
• Breakdown of toxic compounds
• Inorganic transformations that
make available nitrates,
sulphates and phosphates as
well as essential elements such
as Fe and Mn;

33. • N fixation into forms usable by higher
plants.
• Mycorrhizae or root fungi form a
dense network of thin filaments that
reach far into the soil, acting as
extensions of the plant roots they live
on or in.
• Pathogenic microbes are also there
but beneficial is out numbered

34. DESTRUCTION OF SOIL MICROBES
• Natural disturbances
– Wind and water erosion
– Flood
– Fire
– Seasonal changes
• Disturbances due to land
management
– Chemical fertilizers and pesticides used
for cultivation.
– Vehicles used for cultivation

35. • Disturbances associated with
dispersal of waste and
industrial activities.
– Sewage sludge and manure
– Elevated levels of atmospheric
carbon dioxide.
– Plastic wastes

36. Any