• Korean Journal of Soil Science and Fertilizer
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• v.45 no.3
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• pp.428-434
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• 2012

A fungal strain, capable of solubilizing insoluble phosphate under diverse temperature, pH and salt conditions was isolated from Waste Mushroom bed of Agaricus bisporus in South Korea. Based on 18S rRNA analysis, the strain was identified as Aspergillus awamori bxq33110. The strain showed maximum phosphate solubilization in AYG medium (525 ${\mu}g\;mL^{-1}$) followed by NBRIP medium (515 ${\mu}g\;mL^{-1}$). The strain solubilized $Ca_3(PO_4)_2$ to a greater extent and rock phosphate and $FePO_4$ to a certain extent. However $AlPO_4$ solubilizing ability of the strain was found to be very low. Glucose at the rate of 2% ($561{\mu}g\;mL^{-1}$) was found be the best carbon source for Aspergillus awamori bxq33110 to solubilize maximum amount of phosphate. However, no significant difference ($P{\leq}0.05$) in phosphorus solubilization was found between 1% and 2% glucose concentrations. $(NH_4)_2SO_4$ was the best nitrogen source for Aspergillus awamori bxq33110 followed by $NH_4Cl$ and $NH_4NO_3$. At pH 7, temperature $30^{\circ}C$ and 5% salt concentration (674 ${\mu}g\;mL^{-1}$) were found to be the optimal conditions for insoluble phosphate solubilization. However, strain Aspergillus awamori bxq33110 was shown to have the ability to solublize phosphate under different stress conditions at $30-40^{\circ}C$ temperature, pH 7-10 and 0-10% salt concentrations indicating it's potential to be used as bio-inoculants in different environmental conditions.

• Korean Journal of Soil Science and Fertilizer
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• v.45 no.6
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• pp.998-1003
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• 2012

Pantoea agglomerans DSM3493 was isolated from green house soils collected from Chungchugnam-do province, Gongju-Gun area in South Korea and phosphate solubilization and organic acid production of the strain were assessed using three types of insoluble phosphate sources (Ca phosphate, Fe phosphate and Al phosphate) under three different pH conditions (7, 8 and 9). The highest Ca phosphate solubilization ($651{\mu}g\;mL^{-1}$) was recorded at pH 7 followed by pH 8 and 9 (428 and $424{\mu}g\;mL^{-1}$ respectively). The solubilization rate was found to be 80.4, 98.1 and $88.7{\mu}g\;mL^{-1}$ (for Fe phosphate containing medium) and 9.3, 12.1 and $29.8{\mu}g\;mL^{-1}$ (for the Al phosphate containing medium) respectively at pH 7, 8 and 9. Though increasing pH of the medium caused reduction in the rate of solubilization of Ca phosphate, solubilization of Fe and Al phosphates enhanced with increasing pH. By contrast, the highest amount of organic acid was produced with Ca phosphate while the lowest was recorded with the presence of Al phosphate. Among the organic acids, gluconic acid production was found to be the highest, followed by oxalic acid and citric acid regardless the source of phosphate. Results can thus be concluded that the production of organic acids appears to play a significant role in the inorganic phosphate solubilization.

• Journal of Life Science
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• v.11 no.2
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• pp.63-69
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• 2001

bacterium having high abilities to solubilize in-organic phosphate was isolated from cultivated soils. The strain was identified as Aeromonas hydrophila DA33, based on the physiological and biochemical properties. The optimum temperature and initial pH to solubilize insoluble phosphate in sucrose minimal medium were 3$0^{\circ}C$ and pH 5.0, respectively. In these conditions, phosphate-solubilizing activities of the strain against two types of insoluble phosphate were quantitatively determined. When glucose was used for carborn source, the strain had a marked mineral phospahte solubilizing activity. Inorganic phospahte solubilization was directly related to the pH drop by the strain. Analysis of the culture medium confirmed the production of gluconic acid as the main organic acid released by Aeromonas hydrophila DA33.

• Korean Journal of Microbiology
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• v.39 no.1
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• pp.51-55
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• 2003

To develop environment-friendly biofertilizer solubilizing insoluble phosphates, a bacterium possessing a high ability to solubilize $Ca_{3}(PO_{4})_{2}$) was isolated from the rhizosphere of peas. On the basis of its morphological, cultural, physiological characteristics, and Vitek analysis, this bacterium was identified as Pantoea agglomerans. The optimal medium composition and cultural conditions for the solubilization of insoluble phosphate by P. agglomerans R-38 were 3% of glucose.0.1% of TEX>$NH_{4}NO_{3}$, 0.02% of $MgSO_{4}\cdot\7H_{2}O$, and 0.06% of $CaCl_{2}\cdot\2H_{2}O$ along with initial pH 7.5 at $30^{\circ}C$. The highest soluble phosphate production under optimum condition was 898 mg/L after 5 days of cultivation. The solubilization of insoluble phosphate was associated with a drop in the pH of the culture medium. The strain produced soluble phosphate to the culture broth with the concentrations of 698 mg/L against CaHPO$_4$, 912 mg/L against hydroxyapatite, 28 mg/L against $FePO_{4}\cdot\4H_{2}O$, and 19 mg/L against $AIPO_{4}$, respectively.

• Korean Journal of Environmental Agriculture
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• v.26 no.1
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• pp.36-41
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• 2007

Phosphate-solubilizing microorganisms were isolated from soil around Kyungnam and Kyungbook regions using potato dextrose agar-calcium phosphate medium. A fungus with the greatest phosphate-solubilizing activity was selected and identified to Aspergillus sp. PS-104, based on the morphological characteristics of conidiophore and conidia; unbranching type of conidiophore, terminally swelling of conidiophore and septate of mycelium, in malt extract agar and potato dextrose agar media. The optimum temperature and initial pH to solubilize rock phosphate in potato dextrose broth-rock phosphate medium were $30^{\circ}C$ and pH 7.0, respectively. In these optimum conditions, phosphate-solubilizing activities of Aspergillus sp. PS-104 against four twos of insoluble phosphate, tricalcium phosphate, aluminium phosphate, hydroxyapatite and rock phosphate, were quantitatively determined. As result, the maximum phosphate-solubilizing activity was obtained with tricalcium-phosphate (1,900 ppm) while minimum activity was obtained with hydroxyapatite (320 ppm). Futhermore, phosphate-solubilizing activity of Aspergillus sp. PS-104 was found higher when treated with nitrates as compared to the ammonium salts as a nitrogen sources.

• Journal of Life Science
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• v.23 no.2
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• pp.242-248
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• 2013

The objective of this study was to develop a mineral phosphate-solubilizing bacterium as a biofertilizer. A mineral phosphate-solubilizing bacterium HR-1019 was isolated from cultivated soils. It was identified as Bacillus subtilis by 16S rDNA analysis. The phosphate-solubilizing activities of the HR-1019 strain against three types of insoluble phosphate, hydroxyapatite, tri-calcium phosphate, and aluminum phosphate were quantitatively determined. When 5% of glucose concentration was used as a carbon source, the strain showed marked mineral phosphate-solubilizing activity. Mineral phosphate solubilization was directly related to pH drop in the culture solution of the strain. The pathogenic activity and antifungal effects of the HR-1019 strain were measured inclear zones formed in PDA media.

• The Journal of Natural Sciences
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• v.12 no.1
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• pp.69-79
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• 2002

850 strains of phosphate-solubilizing bacteria were isolated from soil of Chung-nam and Daejeon region using 0.5% calcium phosphate containing medium. The HS-2 strain with the highest rock phosphate-solubilizing activity was selected and identified as Azotobacter sp. HS-2 based on the microbiological characteristics. The optimum culture temperature and initial pH of medium for solubilization of rock phosphate were $30^{\circ}C$ and pH 6.0-7.0, respectively. Addition of oxalic acid(0.5M) into the PDB-rock phosphate medium increased 50% solubilization of rock phosphate.

• Journal of Microbiology and Biotechnology
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• v.27 no.4
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• pp.844-855
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• 2017

Phosphate-solubilizing bacteria (PSB) have the ability to dissolve insoluble phosphate and enhance soil fertility. However, the growth and mineral phosphate solubilization of PSB could be affected by exogenous soluble phosphate and the mechanism has not been fully understood. In the present study, the growth and mineral phosphate-solubilizing characteristics of PSB strain Burkholderia multivorans WS-FJ9 were investigated at six levels of exogenous soluble phosphate (0, 0.5, 1, 5, 10, and 20 mM). The WS-FJ9 strain showed better growth at high levels of soluble phosphate. The phosphate-solubilizing activity of WS-FJ9 was reduced as the soluble phosphate concentration increased, as well as the production of pyruvic acid. Transcriptome profiling of WS-FJ9 at three levels of exogenous soluble phosphate (0, 5, and 20 mM) identified 446 differentially expressed genes, among which 44 genes were continuously up-regulated when soluble phosphate concentration was increased and 81 genes were continuously down-regulated. Some genes related to cell growth were continuously up-regulated, which would account for the better growth of WS-FJ9 at high levels of soluble phosphate. Genes involved in glucose metabolism, including glycerate kinase, 2-oxoglutarate dehydrogenase, and sugar ABC-type transporter, were continuously down-regulated, which indicates that metabolic channeling of glucose towards the phosphorylative pathway was negatively regulated by soluble phosphate. These findings represent an important first step in understanding the molecular mechanisms of soluble phosphate effects on the growth and mineral phosphate solubilization of PSB.

• Biotechnology and Bioprocess Engineering:BBE
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• v.7 no.4
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• pp.201-205
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• 2002

The growth conditions of Pantoea aggicmerans, a phosphate solubilizing organism, were studied In our laboratory to determine the optimal conditions. Pantoea aggionerans showed the highest growth rate at 30$\^{C}$, pH 7.0 and 2 vvm, after 50 h cultivation. A certain relationship between pH and phosphate concentration was evident when the glucose concentration in the me dium was changed. Increasing glucose concentration increased the pH buffer action of the broth. At glucose concentrations higher than the optimum concentration of 0.2 M, the cell growth was retarded. P. agglomerans consumed glucose as a substrate to produce organic acids which caused the pH decrease in the culture medium. The phosphate concentration in the medium was increased by the presence of the organic acids, which solubilized insoluble phosphates such as hydroxyapa-tite.

• Korean Journal of Agricultural Science
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• v.49 no.3
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• pp.463-481
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• 2022

Phosphorous (P) is considered to be one of the key essential elements demanded by crop plants. Approximately 70 - 90% of phosphatic fertilizers applied to crops are fixed in soil as Ca, Fe, and Al metal cations, which are insoluble and thus not readily available for plant uptake. Therefore, most soils are deficient in plant available P. This is usually rectified by applying phosphate fertilizers continuously, although this is not economically viable or environmentally acceptable. The present paper reviews the mechanisms involved with phosphate solubilization and mineralization by phosphate solubilizing microorganisms (PSMs) with the associated factors that determine the success. PSMs are effectively involved in mediating the bioavailability of soil P. Their contribution includes mineralization of organic P solubilization of inorganic P minerals, and storing sizable amounts of P in biomass through different mechanisms such as the production of organic and inorganic acids, H₂S, siderophores, exopolysaccharides, and production of enzymes such as phosphatases, phytase, and phosphonatases/C-P lyases, which are capable of chelating the metal ions, forming complexes, and making plant available P. PSMs manifest a wide range of metabolic functions in different environments, resulting in significantly higher plant growth, enhanced soil properties, and increased biological activities. Therefore, development of bio-inoculants with efficient novel PSM strains and further investigations on exploring such strains from diverse ecological niches with multifunctional plant-growth-promoting traits are needed.