ISSN 0367-6315 Korean J. Soil Sci. Fert. 45(4), 602-609 (2012) http://dx.doi.org/10.7745/KJSSF.2012.45.4.602 Evaluation of Phosphate Solubilizing Potential of Three Burkholderia Species Isolated from Green House Soils Buddhi Charana Walpola, June-Seob Song, Mi-Jung Keum, and Min-Ho Yoon* College of Agriculture and Life Sciences, Chungnam National University, Daejeon, 305-764, Korea Burkholderia anthina R-4183, Burkholderia diffusa R-15930 and Burkholderia stabilis LMG 14294 isolated from green house soils (Gongju-Gun area, South Korea) were characterized and their phosphate solubilizing ability was assessed. Under in vitro culture conditions, all three species were proved to be effective in solubilizing phosphates in varying degrees. Strain Burkholderia anthina exhibited the highest phosphate solubilization in NBRIP medium (665 µg ml -1 ) followed by Burkholderia diffusa (630 µg ml -1 ) and Burkholderia stabilis (578 µg ml -1 ). However, solubilization of FePO 4 and AlPO 4 was found to be poor in all the strains. Acidification by means of gluconic and oxalic acids accumulation in the culture medium could be the possible mechanism responsible for phosphate solubilization. Glucose at the rate of 3% was found be the best carbon source for Burkholderia anthina while other two Burkholderia species showed maximum phosphate solubilization at 2%of glucose. In the case of nitrogen sources, ammonium and nitrate were equally effective in solubilizing phosphates by Burkholderia species. Despite a slight decrease in phosphate solubilization observed at increasing temperature, all three Burkholderia species could withstand a temperature of 30-35℃, pH at the range of 7-9 and the presence of NaCl (up to 2.5%) without much compromising the phosphate solubilization. As shown with potted mung bean seedlings, all the three isolates could enhance soil fertility and plant growth indicating their great potential to be used as bio-inoculants. Key words: Phosphate Solubilization, Burkholderia species, Acidification Received : 2012. 7. 18 Accepted : 2012. 8. 16 *Corresponding author : Phone: +82428216733 E-mail: mhyoon@cnu.ac.kr Article Introduction Phosphorus is one of the major essential macronutrients for plant growth and it is applied as chemical fertilizer. However, a large portion of the applied soluble forms of phosphorus fertilizers are easily immobilized in to ins- oluble forms particularly, CaHPO 4 , Ca 3 (PO 4 ) 2 , FePO 4 and AlPO 4 and then become unavailable to plants (Mundra et al., 2011). Therefore, most soils are deficient in soluble forms of phosphorus. This leads to an excess application to crop plants and continuous application of phosphate fertilizers cause economical and environmental problem due to soil and water pollution (Park et al., 2010). There are some microorganisms effectively involved in the solubilization of insoluble phosphate (Vassilev et al., 2006) called as phosphate solubilizing microorganisms (PSMs). Recently, PSMs have attracted the attention of agriculturists to apply them to soil as bio-inoculants to mitigate the phosphate problems (Fasim et al., 2002). Solubilization of phosphate by PSMs depends on various physico-chemical factors viz. nature and amount of phosphate sources, pH, temperature, salt and acid concentration. Apart from this, carbon and nitrogen sources and their concentrations also have strong influence on phosphate solubilization (Dave and Patel, 2003). Therefore effective phosphate solubilization mainly depends on optimum combination of various physico- chemical factors along with the energy sources. Previous studies have demonstrated that the ability of some Burkholderia species to efficiently solubilize inorganic phosphates, which subsequently results in increased availability of phosphorus for plants (Lin et al., 2006; Song et al., 2008). In present study three Burkholderia species having potential to solubilize insoluble phosphates were isolated from green house soils in South Korea and their characteristics of phosphate solubilization were investigated. In addition, the capacity of these isolates as bio-inoculants was assessed in pot experiments.