Categories of Microbial Cultures Based on Function

1. Nitrogen-Fixing Microbes

Nitrogen-fixing microbes play a critical role in converting atmospheric nitrogen into forms usable by plants, reducing dependency on synthetic fertilizers.

• Rhizobium spp.: Symbiotic bacteria forming nodules in leguminous plants like chickpeas, lentils, and soybeans.
• Azospirillum spp.: Free-living bacteria enhancing nitrogen uptake in cereals such as maize, wheat, and sorghum.
• Azotobacter spp.: Non-symbiotic nitrogen-fixing bacteria suitable for a wide variety of crops, including vegetables and sugarcane.
• Frankia spp.: Forms nitrogen-fixing nodules in non-leguminous trees like Casuarina and Alnus.

2. Phosphate-Solubilizing Microbes (PSM)

These microbes release bound phosphates in the soil, increasing phosphorus availability for plants.

• Bacillus subtilis: Effective for cereals, vegetables, and horticultural crops.
• Pseudomonas fluorescens: Promotes root development and enhances phosphorus uptake in diverse crops.
• Penicillium spp.: Efficient fungal phosphate solubilizers for horticultural crops and fruit plants.
• Aspergillus niger: Commonly used for soil amendment in a variety of farming systems.

3. Potassium-Mobilizing Microbes

These microbes solubilize potassium minerals, making them available for plant absorption.

• Frateuria aurantia: Widely used in crops like paddy, sugarcane, and vegetables.
• Bacillus mucilaginosus: Enhances potassium mobilization in cereals and oilseeds.

4. Plant Growth-Promoting Rhizobacteria (PGPR)

PGPR enhance plant growth through mechanisms like hormone production, stress tolerance, and nutrient availability.

• Bacillus amyloliquefaciens: Promotes root elongation and disease resistance.
• Pseudomonas putida: Enhances nutrient uptake and suppresses root pathogens.
• Burkholderia cepacia: Effective in improving growth under stress conditions like drought and salinity.
• Acinetobacter calcoaceticus: Promotes growth in a variety of crops through auxin production.

5. Mycorrhizal Fungi

Mycorrhizal fungi form symbiotic relationships with plant roots, improving water and nutrient absorption.

• Arbuscular Mycorrhizal Fungi (AMF) : Widely used for improving phosphorus uptake in cereals, pulses, and fruit crops.
• Ectomycorrhizal Fungi: Commonly associated with forest trees like pines and eucalyptus.

6. Bio-Pesticides

Bio-pesticides are natural agents used to control pests and diseases, reducing reliance on chemical pesticides.

• Trichoderma viride: Controls soil-borne pathogens like Fusarium and Rhizoctonia.
• Bacillus thuringiensis (Bt) : Targets larvae of pests such as caterpillars and moths in vegetable and cotton crops.
• Metarhizium anisopliae: Fungal bio-pesticide effective against soil-dwelling insects like termites.
• Beauveria bassiana: Controls whiteflies, aphids, and thrips in horticulture.

7. Bio-Control Agents

These microbes protect crops by suppressing harmful pathogens and diseases.

• Pseudomonas fluorescens: Controls bacterial wilt and fungal pathogens in tomatoes and brinjals.
• Trichoderma harzianum: Suppresses damping-off disease in seedlings and root rot in various crops.
• Bacillus subtilis: Works as both a bio-pesticide and a biocontrol agent.

8. Decomposer Microbes

Decomposer microbes aid in breaking down organic material, turning agricultural waste into nutrient-rich compost.

• Cellulomonas spp.: Breaks down cellulose in crop residues.
• Bacillus licheniformis: Aids in degrading lignin and hemicellulose.
• Aspergillus terreus: Effective in composting organic waste rapidly.

9. Stress-Tolerant Microbes

These microbes help plants survive in extreme conditions like drought, salinity, or poor soils.

• Halotolerant Bacillus spp.: Enhances plant growth in saline soils.
• Pseudomonas stutzeri: Improves water uptake in drought-prone conditions.
• Rhizobium sp. (Stress-Adapted) : Ensures nitrogen fixation in sub-optimal environments.
• Arthrobacter spp.: Survives in acidic and nutrient-deficient soils, aiding plant growth.