Phosphorus Solubilization in Soil: How PSB Work
Phosphorus is the second most limiting macronutrient after nitrogen. It is abundant in all agricultural soils — but locked in mineral and organic forms unavailable to plants. Only 1 to 2% of total soil phosphorus is in solution as plant-available forms (HPO₄²⁻, H₂PO₄⁻). The remaining 98% is immobilized by precipitation with calcium (Ca₃(PO₄)₂), iron (FePO₄) and aluminum (AlPO₄), or sequestered in organic matter as phytates. Applied phosphate fertilizer meets the same fate: 75 to 95% is fixed within days. Its real agronomic efficiency rarely exceeds 5 to 25%. The rest is lost, sometimes leached into surface water.
Phosphate-Solubilizing Bacteria (PSB): Four Mechanisms of Action
PSB are soil micro-organisms capable of releasing immobilized phosphorus through four complementary pathways.
1. Acidolysis: strains producing glucose dehydrogenase (gcd/pqq system) oxidize glucose into gluconic acid, releasing H⁺ protons that locally dissolve calcium phosphates: Ca₃(PO₄)₂ + 2H⁺ → 3Ca²⁺ + 2H₂PO₄⁻.
2. Chelation: the -OH and -COOH groups of secreted organic acids capture Fe³⁺, Al³⁺ and Ca²⁺, dissociating metal-phosphate complexes and releasing phosphorus in mobile form.
3. Enzymatic hydrolysis: phytases and phosphatases (acid and alkaline) cleave ester P-O bonds in phytates: Phytate + H₂O → inositol + 6HPO₄²⁻ organic phosphorus represents 30 to 50% of total P in most cultivated soils.
4. Root-bacteria dialogue: the plant releases oxalate, citrate and flavonoids that attract PSB toward the rhizosphere; in return, bacteria regulate PHT1/PHT2 transporters and stimulate root hair growth, maximizing phosphorus uptake.
Three Genera Dominate Solubilization Efficiency
PSB are found in all soil types, but three genera dominate in documented agronomic performance. Bacillus and Priestia (Firmicutes): sporulating, storage-stable, active in greenhouse substrates and field conditions. The species B. subtilis, B. velezensis, B. licheniformis, P. megaterium combine P solubilization, nitrogen fixation and siderophore production. Pseudomonas (Proteobacteria): efficient organic acid producers, particularly active in acidic soils. P. fluorescens, P. putida. Burkholderia (Proteobacteria) are strong phosphatase activity, adapted to tropical soils and organic P-rich substrates (B. vietnamiensis, Paraburkholderia kururiensis).
Ulysse Biotech selected six sporulating strains of Bacillus and Priestia to formulate Éra Boost Pro — a consortium designed to perform in Canadian greenhouse and horticultural production conditions.
Phosphorus
solubilization
in the soil.
How phosphate-solubilizing bacteria (PSB) make phosphorus, locked in minerals and organic matter, available to roots. Ulysse Biotech selected six of these strains to formulate Éra Boost Pro, a high-performance microbial consortium.
Phosphorus is everywhere
in the soil, but almost never available.
An essential macronutrient for photosynthesis, cell division and nitrogen fixation. Yet its concentration in soil solution is only in the micromolar range.
Applied chemical fertilizer is fixed by calcium, iron and aluminum within days: 75–95% of it. Its real efficiency is only 5 to 25%; the rest is lost, sometimes leached into surface water.
The biological solution: recruit soil bacteria capable of releasing trapped phosphorus. These bacteria already exist naturally — the goal is to select, multiply and formulate them.
A microbial community
spread across multiple phyla.
PSB are found in all soil types. Three genera dominate in solubilization efficiency.
P. aeruginosa · P. corrugata
B. velezensis · B. licheniformis
(legume symbiont)
(nitrogen fixation, siderophores)
Paraburkholderia kururiensis
Streptomyces spp.
How PSB release
phosphorus.
In the rhizosphere, bacteria deploy four complementary strategies to activate phosphorus and transfer it to the plant.
Acidolysis: organic acid secretion
PSB oxidize glucose to gluconic acid using their glucose dehydrogenase enzyme (gcd/pqq system). The released H⁺ protons locally acidify the soil and dissolve calcium phosphates.
Chelation: cation capture
The –OH and –COOH groups of organic acids chelate Fe³⁺, Al³⁺ and Ca²⁺. The metal-phosphate complex breaks apart; the released phosphate becomes mobile and plant-available.
Enzymatic hydrolysis: phytase & phosphatases
Organic P accounts for 30–50% of total P, dominated by phytates. PSB secrete phytases and phosphatases (acid or alkaline) that cleave P–O ester bonds.
Root–bacteria dialogue: exudates & PHT
The plant releases oxalate, citrate and flavonoids; these exudates attract PSB. In return, the bacteria regulate PHT1/PHT2 transporters and stimulate root hair growth.
Ulysse Biotech brings
this science to life with Éra Boost Pro.
A six-strain microbial consortium of spore-forming Bacillus and Priestia, formulated to solubilize phosphorus — and more: K, Ca, micronutrients — directly in the rhizosphere.
Available formats
- Six complementary Bacillus & Priestia strains
- Spore-forming, stable for long-term storage
- Forms a beneficial biofilm on roots
- Solubilizes P, K, Ca + releases Zn, Mn, Fe, Cu
A consortium performs
infinitely better than a single strain.
Each strain contributes its specialty (solubilization, fixation, hormones, defense) and all cooperate by forming a protective biofilm on the root.
What Éra Boost Pro
delivers to the plant.
A denser, more branched root system that explores more soil and captures more water and nutrients.
The root biofilm improves substrate water retention and reduces passive evaporation from peat and coco substrates.
Beyond P, the consortium increases the bioavailability of zinc, manganese, iron and copper, critical enzymatic co-factors.
Compatible with liquid and granular fertilizers. Reduces inputs without yield loss: less leaching, less eutrophication.
The microbial biofilm secures the root zone from planting. Bacteria rapidly colonize new roots, limiting stress and accelerating recovery after transplanting.
The strains secrete auxins (growth hormones), enzymes that enhance nutrient uptake, and exopolysaccharides that, much like hyaluronic acid, retain water in the rhizosphere.
The soil holds the phosphorus.
Bacteria hold the key.
Discover how Éra Boost Pro can fit into your growing practices: field crops, vegetables, fruit trees, ornamentals, hydroponics.
- Sun X. et al. (2026) : Phosphate-solubilizing bacteria: a review of diversity, mechanisms, and applications in sustainable agriculture. Front. Microbiol. 17:1778470.
- Timofeeva A., Galyamova M., Sedykh S. (2022) : Prospects for Using Phosphate-Solubilizing Microorganisms as Natural Fertilizers in Agriculture. Plants 11(16): 2119.
- Zhu Y. et al. (2024) : The Role of Phosphate-Solubilizing Microbial Interactions in Phosphorus Activation and Utilization in Plant–Soil Systems. Plants 13(19): 2686.