Module 3

Microbial Role in Soil Fertility and Nutrient Cycling

1. Soil fertility refers to the ability of soil to supply nutrients to plants.
2. Microbial biomass carbon is an indicator of soil microbial activity.
3. Carbon cycle is mediated by decomposers (Bacillus, Aspergillus).
4. Nitrogen cycle – Fixation, ammonification, nitrification, denitrification.
5. Nitrifying bacteria – Nitrosomonas, Nitrobacter.
6. Denitrifying bacteria – Pseudomonas denitrificans, Bacillus subtilis.
7. Sulphur cycle – Thiobacillus thiooxidans converts sulphur to sulphate.
8. Phosphorus cycle – Bacillus megaterium, Aspergillus niger release P.
9. Iron bacteria – Gallionella, Leptothrix.
10. Manganese oxidizers – Pseudomonas, Arthrobacter.
11. Actinomycetes improve soil structure and antibiotic activity.
12. Mycorrhiza helps in nutrient absorption and soil aggregation.
13. Biological nitrogen fixation potential in soil ≈ 20–25 kg N / ha / year (free living).
14. Rhizobium–legume symbiosis contributes 50–100 kg N / ha / year.
15. Blue-green algae fix ≈ 25–30 kg N / ha in rice fields.
16. Azolla–Anabaena system adds 40–60 kg N / ha / season.

Microbial Biocontrol Agents

1. Trichoderma viride / harzianum – Controls soil-borne fungal pathogens.
2. Pseudomonas fluorescens – Antagonistic bacteria effective against wilt and rot.
3. Bacillus subtilis – Produces antibiotics and enzymes for biocontrol.
4. Gliocladium virens – Controls damping-off and root-rot diseases.
5. Beauveria bassiana – Controls white-grub, sugarcane borer, bollworm.
6. Metarhizium anisopliae – Used against termites and locusts.
7. Verticillium lecanii – Controls aphids, whiteflies, mealybugs.
8. Bacillus thuringiensis (Bt) – Produces Cry toxin against caterpillars.
9. Bt kurstaki – Effective against Helicoverpa and Spodoptera.
10. Nucleopolyhedrosis Virus (NPV) – Used against Helicoverpa armigera.
11. Granulosis Virus (GV) – Used against sugarcane early-shoot borer.
12. Neem-based biopesticides contain azadirachtin as active ingredient.
13. Bioherbicides – Colletotrichum gloeosporioides for Parthenium control.
14. Biofumigation – Use of Brassica residues producing isothiocyanates.

Microbes in Waste Management and Biodegradation

1. Biodegradation – Breakdown of organic wastes by microbes.
2. Composting – Aerobic decomposition of organic matter.
3. Vermicomposting – Decomposition by earthworms (Eisenia foetida).
4. Cellulose decomposers – Trichoderma, Aspergillus, Bacillus.
5. Lignin decomposers – Phanerochaete chrysosporium (white-rot fungus).
6. Methanogens (Methanobacterium) produce methane in biogas plants.
7. Biogas production stages – Hydrolysis → Acidogenesis → Methanogenesis.
8. Slurry from biogas plants – Rich in N, P, K.
9. Bio-remediation – Using microbes to clean pollutants (oil spills, heavy metals).
10. Bio-augmentation – Addition of efficient microbes for degradation.
11. Bio-leaching – Extraction of metals by microbes (Thiobacillus ferrooxidans).
12. Phytoremediation – Use of plants to remove contaminants.
13. Biosensors – Microbial systems used for detecting pollutants.
14. Bioplastic (PHA, PHB) – Produced by Alcaligenes eutrophus.

Microbial Products and Applications

1. Antibiotics – Penicillin, Streptomycin, Tetracycline, Chloramphenicol.
2. Enzymes – Amylase (Aspergillus), Protease (Bacillus), Lipase (Candida).
3. Vitamins – Propionibacterium shermanii (Vit B₁₂), Ashbya gossypii (Vit B₂).
4. Amino acids – Corynebacterium glutamicum (Glutamic acid), Brevibacterium (Lysine).
5. Organic acids – Citric (Aspergillus niger), Lactic (Lactobacillus).
6. Bioethanol – Saccharomyces cerevisiae from molasses.
7. Biodiesel – Produced by microbial trans-esterification of oils.
8. Biohydrogen – Produced by Clostridium and cyanobacteria.
9. Microbial pigments – Monascus (red pigment), Spirulina (phycocyanin).
10. Microbial polysaccharides – Xanthan gum (Xanthomonas campestris).
11. Microbial inoculant quality control – BIS code – IS (2001).
12. Rhizobium inoculant standard – Minimum 10⁸ CFU / g (6 months shelf life).
13. Liquid biofertilizer pH – 6.5 – 7.5.
14. Biofertilizer mother culture – Pure strain maintained on YEMA medium.
15. CFU stands for – Colony Forming Unit.
16. Biofertilizers and biopesticides are eco-friendly and sustainable inputs.