Biotechnological Tools for Enhancing Microbial Solubilization of Insoluble Inorganic Phosphates

During recent years, many studies appeared on microbial solubilization of insoluble phosphates as an alternative of chemically based P-fertilizer production and bearing in mind the progressive increase in P-fertilizer prices based on high global P consumption and the scarcity of rock phosphate reserves. This biotechnological approach is mainly related to microbial production of organic acids such as citric, oxalic, gluconic, itaconic, and lactic acid, which react with the insoluble P-sources. The most applied and studied P-solubilizers are fungal microorganisms cultivated in conditions of submerged and solid-state fermentation systems. Therefore, the aim of this review is to summarize data on the effect of various abiotic factors on the fungal organic acid production. Nutrient medium components, fermentation process parameters, interaction between insoluble P-particles and microbial systems, and mode of fermentation are analyzed for their impact on both organic acid production and P-solubilization. Suggestions for further studies are also discussed.