SOIL MICROBIOLOGY

POOJA S NATHANS3 BT 44

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

SOIL SAMPLE UNDER MICROSCOPE

MICROBIAL DISTRIBUTION IN SOIL

Earthworms12%

other macro fauna5%

Bacteria and Acti-

nomycetes40%

Other micro flaura(eg:fu

ngi and algae)40%

Mesofauna3%

1.BACTERIA

• 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)

RHIZOSPHERE

• 1/10 inch.• Exudates: carbohydrates

and proteins secreted by roots.

• Attracts bacteria, fungi, nematodes, protozoa.

Rhizosphere

EXAMPLES: :

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

PICS:

2.ACTINOMYCETES

• 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.

• 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

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

EXAMPLES:

• Nocardia asteroides• Dermatophilus congolensis• Streptomyces etc.

PICS:

3.FUNGI

• 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.

• 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.

EXAMPLES:

1.Saprophytic fungi (decomposers) – Pleurotus ostreatus (oyster mushroom)– Lentinula edodes (shiitake) – Stropharia rugosoannulata (king

Stropharia).

2. Mutualists Fungi– Zygomycota – Basidiomycota

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

PICS:

4.ALGAE

• 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.

EXAMPLES:

• Cyanophyta (Blue-green algae) • Chlorophyta (Grass-green algae) • Xanthophyta (Yellow-green algae) • Bacillariophyta (diatoms or golden-

brown algae)

PICS:

5.PROTOZOA

• 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.

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

EXAMPLES:

• Flagellates– (e.g., Giardia lamblia)

• Amoeboids– (e.g., Entamoeba histolytica)

• Sporozoans– (e.g., Plasmodium knowlesi)

PICS:

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;

• 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

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

• Disturbances associated with dispersal of waste and industrial activities.– Sewage sludge and manure– Elevated levels of atmospheric

carbon dioxide.– Plastic wastes

Any Questions ?