Bacillus subtilis

Introduction

Bacillus subtilis is widely used in composting and soil amendment processes due to its ability to decompose organic matter and enhance microbial succession. Its robust enzyme secretion capabilities allow it to break down plant residues, manures, and fibrous waste, converting them into stable, humus-rich compost. It is often included in compost starter cultures, fortified composts, and compost teas.

Scientific Description

Bacillus subtilis is a gram-positive, rod-shaped, aerobic bacterium that forms highly resilient spores, allowing it to survive fluctuating temperatures and moisture levels in compost heaps. It belongs to the phylum Firmicutes and is known for producing a broad spectrum of extracellular enzymes including cellulases, xylanases, amylases, and proteases.

Key traits:

• Thermotolerance: Can survive and function in mesophilic to early thermophilic stages of composting.
• Enzyme Production: Breaks down lignocellulosic residues, starches, proteins, and complex organics.
• Aerobic Decomposition: Enhances oxygenation by stimulating microbial aeration pathways.
• Antagonistic Behavior: Suppresses putrefactive and pathogenic microbes during decomposition.

Benefits

• Accelerates Compost Maturation: Reduces composting time by rapidly degrading organic matter.
• Improves Nutrient Cycling: Converts unavailable forms of nitrogen and phosphorus into plant-available forms.
• Controls Odor and Pathogens: Inhibits foul-smelling anaerobes and harmful microbes.
• Increases Microbial Diversity: Enhances succession of beneficial decomposers in compost piles.
• Survives Harsh Conditions: Spore-forming ability ensures survival through dry or hot phases of composting.

Uses

• Organic Waste Types: Crop residues, vegetable peels, spent mushroom beds, manure, sugarcane trash, kitchen waste.
• Application Methods:
  • Compost starter: Mix 1–2 kg (dry) or 1–2 L (liquid) per ton of composting material.
  • Compost tea: Added to brewed compost extract for foliar sprays or soil drenching.
  • Farmyard manure enrichment: Blended with cow dung and straw for high-nitrogen fortified manure.
• Best Conditions: Moist, aerobic piles with C:N ratios of 25–30:1; functions well from 20–45°C.

Trivia

• First isolated over 100 years ago, it’s one of the most studied model bacteria in science.
• Known for producing antibiotics like subtilin, which contribute to pathogen suppression in compost.
• Used in probiotics for livestock and aquaculture, showcasing its environmental safety.
• Often paired with Trichoderma and Phosphobacteria in composting consortia.