Quantification of soil microflora and role of microorganisms in soil fertility

1. VIVEKANANDHA ARTS AND SCIENCE COLLEGE FOR WOMEN
VEERACHIPALAYAM - 636007
SANGAKIRI,SALEM,TAMILNADU.
DEPARTMENT OF MICROBIOLOGY
SUBMITTED BY;
E.ANU
I -MSC MICROBIOLOGY
DEPARTMENT OF MICROBIOLOGY
VIAAS, SANGAKIRI
GUIDED BY
Dr.R.DINESHKUMAR,
AP/MICROBIOLOGY,
DEPARTMENT OF MICROBIOLOGY,
VIVEKANANDHA ARTS AND SCIENCE
COLLEGE FOR WOMEN, SANKAGIRI,
SALEM, TAMILNADU
SUBJECT:SOIL AND ENVIRONMENTAL MICROBIOLOGY
TOPIC:SOIL MICROFLORA

2. CONTENT
● SOIL MICROFLORA
● FUNCTION
● QUANTIFICATION
● METHODS
● SOIL FERTILITY
● ROLE OF MICROORGANISMS IN SOIL
FERTILITY

3. Soil microflora refers to the diverse community of microscopic
organisms, including bacteria, fungi, algae, and protozoa, that inhabit the soil. These
microorganisms play a crucial role in maintaining soil health and supporting various
ecosystem services, such as nutrient cycling, decomposition of organic matter, and
plant growth.
TYPES OF SOIL MICROFLORA:
1.Bacteria
2.Fungi
3.Actinomycetes
4.Algae
SOIL MICROFLORA

4. FUNCTION
❖ Decomposition: Breakdown of organic matter into humus.
❖ Nutrient cycling: Transformation of nitrogen, phosphorus,
sulfur.
❖ Soil structure improvement: Microbial byproducts bind soil
particles.
❖ Plant growth promotion:
Nitrogen fixation (e.g., Rhizobium, Azotobacter)
Phosphate solubilization.
Production of growth hormones.
❖ Disease suppression: Some microbes inhibit plant pathogens

5. QUANTIFICATION OF SOIL MICROFLORA
Quantifying soil microflora involves measuring the abundance
and types of microorganisms present in soil, including bacteria, fungi, and other
microbes. This is crucial for understanding soil health, nutrient cycling, and
ecosystem functioning. Several methods are employed, including cultivation-
based techniques, molecular biology approaches, and biochemical analyses.
METHODS:
● Direct microcopy method
● Clture based methods
● Molecular Techniques
● Biochemical

6. 1. DIRECT MICROSCOPY:
Soil samples are mixed with a suspending solution, stained with dyes like
acridine orange or DAPI (4',6-diamidino-2-phenylindole), and observed under a
microscope, often a fluorescence microscope. The dyes bind to nucleic acids,
making the microorganisms visible.
Advantages: It's relatively quick and can provide an estimate of the total microbial
count, including bacteria, fungi, and protozoa.
Disadvantages: It doesn't differentiate between living and dead cells, and it can be
challenging to distinguish between different types of microorganisms. Also, the
presence of soil particles can interfere with the counting process.

7. 2.CULTURED -BASED METHOD:
Soil samples are serially diluted and spread onto agar plates
containing specific growth media. These media are designed to support the
growth of different microbial groups (e.g., bacteria, fungi). After incubation, the
number of colonies that grow on the plates is counted, and the results are
expressed as colony-forming units per gram of soil (CFU/g).
Advantages: This method allows for the isolation and identification of specific
microorganisms. It provides information about the viable (living) microbial
population.
Disadvantages: It's selective, meaning that only the microorganisms that can
grow on the specific media will be counted. Many soil microorganisms are
difficult or impossible to culture in the lab, leading to an underestimation of the
total microbial population.

8. 3.Molecular Techniques:
● DNA extraction: DNA is extracted from soil
● PCR amplification: Specific genes (e.g., the 16S rRNA gene for bacteria and archaea, or the ITS region
for fungi) are amplified using PCR.
Quantification:
● qPCR: Uses fluorescent dyes or probes to quantify the amount of the amplified DNA, providing an
estimate of the abundance of specific microbial groups
● DNA sequencing: The amplified DNA is sequenced, and the sequences are compared to databases to
identify and quantify different microbial taxa.
Advantages: These methods are highly sensitive and specific, allowing for the detection and quantification
of a wide range of microorganisms, including those that are difficult or impossible to culture. They provide
detailed information about the composition and diversity of the microbial community.
Disadvantages: They can be more expensive and technically complex than culture-based methods. The
accuracy of the results depends on the quality of DNA extraction and the specificity of the primers used in
PCR.

9. 4.BIOCHEMICAL:
These assays measure the activity of enzymes or the rate of
substrate utilization in soil samples. For example, the activity of enzymes
involved in carbon, nitrogen, or phosphorus cycling can be measured.
Alternatively, the rate of respiration (CO2 production) or the rate of substrate
(e.g., glucose) consumption can be measured.
Advantages: They provide information about the functional activity of the
microbial community, which can be related to nutrient cycling and other soil
processes.
Disadvantages: These assays may not directly quantify the number of
microorganisms. The activity of enzymes can be affected by various factors,
such as soil pH, temperature, and the presence of inhibitors.

10. SOIL FERTILITY
Soil fertility refers to the ability of soil to provide
essential nutrients to plants in adequate amounts and proper balance
for their healthy growth and reproduction.
1.Rich in nutrients (N, P, K, Ca, Mg, S, etc.)
2. Good soil structure (porous, well-aerated)
3. Adequate organic matter (humus)
4. Proper pH level (usually 6.0–7.5
5. Presence of beneficial microorganisms
6.Good water-holding capacity
7. Low level of toxic substances

11. Role of Microorganisms in soil
Fertility

12. 1.Decomposition of Organic Matter
❖ Microbes involved: Bacteria, fungi, actinomycetes
❖ Process:Break down plant residues, dead organisms, and organic
waste.
❖ Convert complex substances (cellulose, lignin, proteins) into simpler
forms like CO₂, water, and humus.
Benefits:
● Releases nutrients (N, P, S) in plant-available forms.
● Forms humus, which improves soil texture and water-holding
capacity.
ROLE OF MICROORGANISMS

13. 2.Nutrient Cycling
Microbes mediate all major biogeochemical cycles:
A. Nitrogen Cycle
● Nitrogen fixation:
Rhizobium (symbiotic in legumes)
Azotobacter, Clostridium (free-living)
Frankia (actinorhizal symbionts)
Convert atmospheric N₂ into ammonia (NH₃), usable by plants.
● Nitrification:
Nitrosomonas NH₄⁺ to NO₂⁻
→
Nitrobacter NO₂⁻ to NO₃⁻
→

14. ● Denitrification:
Pseudomonas, Paracoccus reduce NO₃⁻ to N₂
gas, balancing excess nitrogen.
B.Phosphorus Solubilization
● Phosphate-solubilizing bacteria (PSB): Bacillus, Pseudomonas
● Solubilize insoluble phosphate (e.g., tricalcium phosphate) into soluble
forms (H₂PO₄⁻).
C. Sulfur and Potassium Cycling
● Thiobacillus oxidizes sulfur to sulfates.

15. 3. Biological Nitrogen Fixation (BNF):
● Microorganisms fix atmospheric nitrogen without chemical
fertilizers.
● Legume–Rhizobium symbiosis enriches soil nitrogen.
● Reduces dependency on synthetic nitrogen fertilizers.
4.Disease Suppression:
Antagonistic microbes:Trichoderma, Pseudomonas fluorescens
inhibit soil-borne pathogens(e.g., Fusarium, Rhizoctonia).
Mechanisms: competition, antibiosis, parasitism.

16. 5. Plant Growth Promotion:
● PGPR (Plant Growth-Promoting Rhizobacteria):
e.g., Azospirillum, Bacillus subtilis, Pseudomonas spp.
Functions:
Produce phytohormones (IAA, gibberellins)
Enhance nutrient uptake
Induce systemic resistance (ISR) in plants
6.Soil Structure and Aggregation
Fungi (like mycorrhizae) and bacteria produce polysaccharides
and glomalin, which:
● Bind soil particles into stable aggregate
● Improve aeration, water infiltration, and root penetration

17. 7. Mycorrhizal Associations:
● Arbuscular Mycorrhizal Fungi (AMF):
● Form symbiotic relationships with ~80% of plants
● Extend root absorption area via hyphae
● Improve uptake of phosphorus, zinc, copper, and water
● Enhance drought and salt tolerance
8. Bioremediation and Detoxification
● Microbes degrade pesticides, heavy metals, and pollutants in soil.
● Maintain fertility by preventing toxicity buildup.

18. 9.Biortilizer Production
● Microbes are used to produce biofertilizers:
● Nitrogen fixers (Rhizobium, Azospirillum)
● Phosphate solubilizers (Bacillus, Aspergillus)
● Potassium solubilizers
● Mycorrhizal inoculants

19. Thank you