Phosphate-Solubilizing Microorganisms: Mechanism and Their Role in Phosphate Solubilization and Uptake

Abstract

Phosphorus is the second most critical macronutrient after nitrogen required for metabolism, growth, and development of plants. Despite the abundance of phosphorus in both organic and inorganic forms in the soil, it is mostly unavailable for plant uptake due to its complexation with metal ions in the soil. The use of agrochemicals to satisfy the demand for phosphorus to improve crop yield has led to the deterioration of the ecosystem and soil health, as well as an imbalance in the soil microbiota. Consequently, there is a demand for an alternate cost-effective and eco-friendly strategy for the biofortification of phosphorus. One such strategy is the application of phosphate-solubilizing microorganisms which can solubilize insoluble phosphates in soil by different mechanisms like secretion of organic acids, enzyme production, and excretion of siderophores that can chelate the metal ions and form complexes, making phosphates available for plant uptake. These microbes not only solubilize phosphates but also promote plant growth and crop yield by producing plant-growth-promoting hormones like auxins, gibberellins, and cytokinins, antibiosis against pathogens, 1-aminocyclopropane-1-carboxylic acid deaminase which enhances plant growth under stress conditions, improving plant resistance to heavy metal toxicity, and so on. Pyrroloquinoline quinine (pqq) and glucose dehydrogenase (gcd) are the representative genes for phosphorus solubilization in microorganisms. The content presented in this review paper focuses on different mechanisms and modes of action of phosphate-solubilizing microorganisms, their contribution to phosphorus solubilization, growth-promoting attributes in plants, and the molecular aspects of phosphorus solubilization.

Review of Phosphite as a Plant Nutrient and Fungicide

“…Phosphate solubilizing microorganisms (PSMs) represent microflora important to organic P mineralization, solubilizing inorganic P minerals, and storing large amounts of P in microbial biomass. Rawat et al [42] documented the diversity in PSMs in soil including over 40 bacteria, cyanobacteria, and actinomycetes and 15 fungi including several vesicular arbuscular mycorrhizae. PSMs exude phosphatase enzymes, chelates, and organic acids, with a concomitant decrease in soil pH to solubilize (oxidize) soil P into plant available Pi.…”

Utilization of soil residual phosphorus and internal reuse of phosphorus by crops

“…Arai & Sparks (2007) found that rhizosphere acidification was an effective way to help obtain mobile P from calcareous soils. Additionally, the organic acids (like citric acid, gluconic acid, oxalic acid, and tartaric acid) (Rawat et al, 2020), inorganic acids (like hydrochloric acid, sulfuric acid, nitric acid, and carbonic acid) and H 2 S production by phosphate-solubilizing microorganisms have been reported to solubilize inorganic phosphate, although inorganic acids have low efficiency compared to organic acids (Gaind, 2016). (2) The cation-anion exchange balance, organic anion and proton extrusion, which lower soil pH to dissolve insoluble phosphates.…”

“…The utilization of organic P also plays a major role in the use of soil residual P. Organic P in soils generally accounts for 20-30% of the total residual P and in some cases accounts for 95% (Rawat et al, 2020). The vast majority of soil organic P is held by a single or double lipid bond, which can be divided into inositol (mainly from plant residue), nucleic acid (from plant and soil organism residue) and phospholipid (from plant, soil animal and microbial residue) forms (Betencourt et al, 2012).…”

“…The interaction of phosphate-solubilizing microorganisms (Pseudomonas, Mycobacterium, Bacillus, Pantoea Rhizobia and Burkholderia) and phosphate fertilizer improve wheat grain yield by 22% and P uptake by 26%, while reduce fertilizer input by 30%. Moreover, these biofertilizers are safe and non-toxic to the environment (Rawat et al, 2020). In addition, transgenic technology has also been used in phosphate-solubilizing microorganisms to achieve efficient utilization of P resources.…”

“…Phosphorus (P), a key component of nucleic acids, phospholipids and adenosine triphosphate (ATP), participates in various assimilatory and metabolic processes in plants (Rawat et al, 2020). Plant growth and productivity are limited by soil P availability, which ultimately affects material circulation and function of ecosystems (Agren, Wetterstedt & Billberger, 2012).…”