Microbiology and Biotechnology Research: An Overview Vol. 9

Phosphorus is a non-substitutable macronutrient that is frequently unavailable to plants because it becomes fixed in soil as sparingly soluble calcium, iron, and aluminium compounds or is retained within organic matter. Phosphate-solubilising fungi (PSF) have been proposed as an economical and environmentally compatible complement to inorganic phosphorus fertiliser, converting fixed phosphorus into forms that plant roots can absorb through organic acid excretion, proton extrusion, and the enzymatic mineralisation of organic phosphorus. This review critically synthesises the peer-reviewed evidence on the taxonomic diversity, biochemical mechanisms, environmental determinants, and agronomic performance of PSF, moving beyond descriptive cataloguing to evaluate the strength, consistency, and methodological quality of the supporting literature. The evidence indicates that solubilisation capacity is taxonomically concentrated within a small number of genera, most consistently Aspergillus and Penicillium, and that in vitro solubilisation assays reliably demonstrate organic acid production and phosphate release under acidic, carbon-rich culture conditions. Translation of this laboratory capacity into consistent field-scale yield benefit is considerably less certain: multi-year field trials of the most commercially advanced fungal inoculant, Penicillium bilaiae, report modest and variable yield increases that depend strongly on baseline soil phosphorus status, while a formal critical assessment of the wider phosphate-solubilising microorganism literature has questioned whether solubilisation capacity measured in culture reliably predicts plant-available phosphorus release in structured, competitive soil environments. Additional applications in salinity amelioration and heavy-metal immobilisation show mechanistic promise but remain supported chiefly by short-term, single-site, or laboratory-scale studies. Persistent limitations across the literature include correlational rather than causal inference regarding the relationship between medium pH and organic acid production, restricted geographic and taxonomic sampling, and inconsistent reporting of strain identity, formulation, and application rate. Future research priorities include standardised and comparable solubilisation assays, mechanistically linked field trials that measure organic acid production alongside yield outcomes, and genomic characterisation of solubilisation pathways, so as to clarify which fungal traits translate reliably into agronomic benefit rather than remaining confined to laboratory demonstration.