Pseudomonas fluorescens (Composting)

Introduction

Pseudomonas fluorescens is a versatile soil and rhizosphere bacterium with important functions during the compost curing stage. While not a primary degrader, it plays a crucial role in nitrogen retention, pathogen suppression, and enhancement of compost quality. Its application toward the end of composting helps enrich the microbial community, prevent nitrogen loss via volatilization, and fortify the compost with plant-beneficial traits.

Scientific Description

P. fluorescens is a gram-negative, aerobic, rod-shaped bacterium that produces a fluorescent pigment (pyoverdine) under iron-limited conditions. It belongs to the Pseudomonadaceae family and is well adapted to colonizing decaying organic matter and plant roots. In composting, it thrives during the mesophilic and curing phases, when the temperature has decreased but microbial competition is still active.

Functional traits in compost:

• Ammonia Scavenging: Competes with ammonia-oxidizers, helping conserve organic nitrogen forms.
• Siderophore Production: Sequesters iron, limiting the growth of spoilage and pathogenic fungi.
• Pathogen Antagonism: Produces antibiotics like phenazine and DAPG to suppress Fusarium, Rhizoctonia, and Sclerotinia.
• Enzymatic Activity: Contributes cellulases and proteases to complete the breakdown of residual organic matter.

Benefits

• Reduces Nitrogen Loss: Helps retain nitrogen during curing by limiting ammonia volatilization and nitrate leaching.
• Suppresses Compost Pathogens: Outcompetes and inhibits harmful microbes that may colonize partially cured compost.
• Improves Final Compost Quality: Enhances microbial diversity and plant growth-promoting potential of finished compost.
• Safe for Use: Non-toxic to plants, compatible with organic standards, and beneficial to the rhizosphere.
• Prepares Compost for Soil Application: Creates a microbe-rich compost more ready for interaction with plant roots.

Uses

• Compost Types: Farmyard manure, green waste compost, food waste compost, coir pith compost, enriched vermicompost.
• Application Methods:
  • Curing stage inoculation: Apply 1–2 kg (powder) or 1–2 L (liquid) per ton of compost, 10–15 days before use
  • Compost tea formulation: Brew with compost for 24–48 hours and apply to soil or as foliar spray
  • Integrated use: Often used with Trichoderma and Bacillus subtilis in commercial compost enrichment kits
• Best Conditions: Mesophilic phase (25–35°C), moisture 50–60%, aerobic piles

Trivia

• Its fluorescent pigment under UV light is used as a marker in compost quality research.
• In some countries, P. fluorescens-inoculated compost is used in nursery trays to reduce seedling damping-off.
• Also contributes to the “microbial priming effect” when compost is added to degraded soils.
• Used in disease-suppressive composts, especially for vegetable nurseries and greenhouse beds.