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
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%
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.
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
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.
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.
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.
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
