Application of phosphate-solubilizing bacteria for enhancing bioavailability and phytoextraction of cadmium (Cd) from polluted soil Seulki Jeong a , Hee Sun Moon b,⇑ , Kyoungphile Nam a , Jae Young Kim a , Tae Sung Kim c a Dept. of Civil and Environmental Engineering, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, South Korea b School of Earth and Environmental Sciences, Seoul National University, 1 Gwanak-ro, Gwanak-gu, Seoul 151-742, South Korea c Haechun ETS Co. Ltd., 169-12 Geumam-dong, Gyeryongsi, Chungnam 321-900, South Korea article info Article history: Received 21 October 2011 Received in revised form 2 March 2012 Accepted 2 March 2012 Available online 1 April 2012 Keywords: Phytoremediation Phosphate-solubilizing bacteria Brassica juncea Abutilon theophrasti Cadmium abstract In this study, phosphate-solubilizing bacteria (PSB), Bacillus megaterium, were used to enhance Cd bio- availability and phytoextractability of Cd from contaminated soils. This strain showed a potential for directly solubilizing phosphorous from soils more than 10 folds greater than the control without inocu- lation. The results of pot experiments revealed that inoculation with B. megaterium significantly increased the extent of Cd accumulation in Brassica juncea and Abutilon theophrasti by two folds relative to the unin- oculated control. The maximum Cd concentrations due to inoculation were 1.6 and 1.8 mg Cd g À1 plant for B. juncea and A. theophrasti after 10 wk, respectively. The total biomass of A. theophrasti was not sig- nificantly promoted by the inoculation treatment, yet the total biomass of B. juncea increased from 0.087 to 0.448 g. It is also worth to mention that B. juncea predominantly accumulates Cd in its stems (39%) whereas A. theophrasti accumulates it in its leaves (68%) after 10 wk. The change of the Cd speciation indi- cated that inoculation of B. megaterium as PSB increased the bioavailabilty of Cd and consequently enhanced its uptake by plants. The present study may provide a new insight for improving phytoreme- diation using PSB in the Cd-contaminated soils. Ó 2012 Elsevier Ltd. All rights reserved. 1. Introduction Soil contamination with heavy metals is becoming one of the most severe environmental issues as they cannot be degraded, but can persist in soil environments (Jiang et al., 2008; Ma et al., 2009). Among heavy metals, Cd is one of the most toxic contami- nants in soils and is a non-essential element for biological meta- bolic functions in plants and animals (Sheng et al., 2008a). Thus, the accumulation of Cd in soils can pose a threat to food safety and is a potential health risk (Dell’Amico et al., 2005). To date, many methods have been developed to remediate Cd-con- taminated soils, including a range of conventional physical and chem- ical engineering technologies that are often expensive and involve substantial excavation and transportation (Suresh and Ravishankar, 2004). These processes often employ stringent physicochemical agents, which have a negative impact on an ecosystem (Lasat, 2002). Phytoremediation has been considered as a novel environment- friendly technology, which uses plants to remove or immobilize heavy metals (Suresh and Ravishankar, 2004). Phytoremediation of- fers benefits over physical and chemical approaches for removing heavy metals from soils in terms of cost and safety to humans and environments (Suza et al., 2008). Several studies have been demonstrated to remediate Cd from soil using phytoextraction (Chen et al., 2010; Luo et al., 2011). However, most plants that could accumulate high concentrations of heavy metals (i.e., hyperaccu- mulator) are not suitable for field applications due to their small biomass and slow growth (Sheng et al., 2008a). In addition, low bio- availability of heavy metals in soils may also limit the efficiency of phytoremediation (Sheng and Xia, 2006; Jiang et al., 2008). The bioavailability of metals can be enhanced by using chemical chelates such EDTA, however, these compounds can increase the metal leaching risk and have negative effects on soil fertility or soil structures (Khan et al., 2000). To avoid these problems, the applica- tion of plant growth promoting rhizobacteria (PGPR) can be consid- ered as an important phytoremediation technology for enhancing biomass production as well as tolerance of the plants to heavy met- als (Chen et al., 2010; Luo et al., 2011). A number of studies have demonstrated the importance of bacterial inoculation for plant sur- vival in heavy metal-polluted environments (Compant et al., 2005; Sheng et al., 2008b; Chen et al., 2010; Luo et al., 2011). The PGPRs stimulate plant growth by producing growth hormones, solubilizing phosphate, fixing nitrogen, and producing siderophore (Compant et al., 2005; Chakraborty et al., 2006). In particular, phosphate-sol- ubilizing bacteria (PSB) are often used to facilitate P dissolution for plant growth from inorganic and organic pools of total soil P by means of phosphate enzyme and organic acid production (Hilda and Fraga, 1999; Chen et al., 2006). 0045-6535/$ - see front matter Ó 2012 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.chemosphere.2012.03.013 ⇑ Corresponding author. Tel.: +82 2 880 6645; fax: +82 2 873 3647. E-mail address: hmoon@snu.ac.kr (H.S. Moon). Chemosphere 88 (2012) 204–210 Contents lists available at SciVerse ScienceDirect Chemosphere journal homepage: www.elsevier.com/locate/chemosphere