Bacillus megaterium

Introduction

Bacillus megaterium is a naturally occurring soil bacterium widely recognized for its ability to solubilize inorganic phosphorus in the soil and make it accessible to plants. Phosphorus is essential for root development, flowering, and energy transfer, yet a large portion of soil phosphorus remains locked in insoluble forms. B. megaterium plays a key role in unlocking this reserve, making it indispensable in low-phosphorus or heavily fertilized but phosphorus-fixed soils.

Scientific Description

Bacillus megaterium is a large, rod-shaped, gram-positive, spore-forming bacterium. It thrives in a wide range of soil conditions and is known for producing organic acids that convert insoluble phosphates (like tricalcium phosphate, rock phosphate) into soluble orthophosphate that plants can absorb.

Key biological traits:

• Phosphate Solubilization: Produces gluconic, citric, and lactic acids that release phosphorus from bound complexes.
• Spore-forming: High environmental resilience; survives drought, high temperatures, and UV exposure.
• PGPR Functionality: Also produces growth-promoting substances such as auxins and siderophores, enhancing root architecture and micronutrient uptake.
• Biocompatible: Functions well in consortiums with nitrogen fixers and mycorrhiza.

Benefits

• Solubilizes Insoluble Phosphorus: Enhances availability of native or applied rock phosphate in the soil.
• Improves Root Development: Boosts root elongation and lateral spread through better phosphorus availability.
• Increases Flowering and Fruit Set: P is critical in reproductive phases, and its availability improves overall yield.
• Enhances Soil Health: Encourages microbial activity and better nutrient cycling.
• Stress Tolerance: Indirectly aids drought resilience via improved root mass and osmotic regulation.

Uses

• Crops Benefited: Universally beneficial — cereals, legumes, vegetables, oilseeds, and fruit crops.
• Application Methods:
  • Seed treatment: 5–10 g/kg seed
  • Soil application: 2–5 kg/acre mixed with compost or FYM
  • Drip irrigation: Liquid inoculants are suitable for fertigation
• Best With: Soils with high phosphorus fixation (e.g., red, lateritic, calcareous soils)
• Compatible With: Rhizobium, Azospirillum, Frateuria, and mycorrhiza (VAM) in biofertilizer cocktails

Trivia

• The name “megaterium” refers to its unusually large cell size — among the largest of all known bacteria.
• Originally isolated in the early 1900s, it’s now a model organism in industrial fermentation as well as agriculture.
• Besides phosphate solubilization, it’s also used in biotechnology to produce enzymes, vitamins, and antimicrobials.