Metal mobilization and production of short-chain organic acids by rhizosphere bacteria associated with a Cd/Zn hyperaccumulating plant, Sedum alfredii

Abstract

Sedum alfredii, a cadmium (Cd) and zinc (Zn) hyperaccumulator at a mine located in Qu Zhou City, Zhejiang Province, China, can accumulate Cd and Zn exceeding 1,000 and 10,000 mg kg −1 , respectively in its shoot (dry weight) when growing under metal-contaminated habitats. Several strains of bacteria were isolated from the rhizosphere of S. alfredii thriving in different Pb/Zn mines in Hunan Province and Zhejiang Province, China, which can resist high levels of heavy metals. Among the different strains isolated, Burkholderia cepacia showed the highest ability in mobilizing Cd and Zn as well as resisting high concentrations of soluble Zn (500 mg L −1 ). The soluble Zn concentration in the medium increased from 13 to 72 and 99% (p<0.001) after bacterial inoculation in the medium supplemented with insoluble zinc oxide and zinc carbonate, respectively, while pH dropped from 7 to 2.93. The soluble Cd concentration was also increased from 8 to 96% (p<0.001), and pH decreased from 7 to 2.65. Short-chain organic acids were also analyzed and the results indicated that oxalic acid, tartaric acid, formic acid and acetic acid had a significant correlation (p< 0.001) with the concentrations of Cd and Zn being mobilized during the assay. The present results implicated that certain bacteria associated with metal hyperaccumulators could contribute significantly in mobilizing heavy metals, which would enhance the phytoextraction process.

Bacterially Induced Weathering of Ultramafic Rock and Its Implications for Phytoextraction

“…Indirectly, they affect weathering rates by complexing ions in solution, thus lowering the solution saturation rate (34). The production of organic acid anions by bacterial strains was related to the weathering of hornblende (35) and the mobilization of metals from carbonates and oxides (13). In the present study, oxalate production seems to have an important role in the solubilization of Mn and Ni.…”

“…Quantin et al (12) showed that bacterial reduction of oxides led to the solubilization of Fe, Mn, Ni, and Co and modified metal distribution in the soil. Li et al (13) related the production of short-chain organic acids by rhizosphere bacteria to the mobilization of Cd and Zn. Cell-free culture filtrates of rhizobacterial strains have been shown to mobilize soil Ni (8,9), Zn, and Cd (6,14).…”

Contaminación Ambiental Por Metales Pesados en México: Problemática Y Estrategias De Fitorremediación

“…Algunas bacterias rizosféricas tienen la capacidad de solubilizar fosfatos debido a la producción de ácidos orgánicos de bajo peso molecular (Gupta et al 2002), entre los cuales están los ácidos fórmico, acético, succínico, tartárico y oxálico (Li et al 2010). Se ha demostrado que los ácidos orgánicos excretados por las bacterias rizosféricas también tienen efecto en la movilización de metales como el Pb, Ni, Cu, Cd y Zn (Fasim et al 2002, Arwidsson et al 2010, Li et al 2010.…”

“…Se ha demostrado que los ácidos orgánicos excretados por las bacterias rizosféricas también tienen efecto en la movilización de metales como el Pb, Ni, Cu, Cd y Zn (Fasim et al 2002, Arwidsson et al 2010, Li et al 2010. Esto se asume debido a la excreción de los ácidos orgánicos al suelo que ocasiona una disminución del pH (Sheng y Shia 2006), que a su vez libera los cationes metálicos al medio.…”

Changes in metal availability, desorption kinetics and speciation in contaminated soils during repeated phytoextraction with the Zn/Cd hyperaccumulator Sedum plumbizincicola

“…The secretions of hyperaccumulator roots can enhance metal availability by decreasing soil pH or forming soluble DOM-metal complexes (Dessureault-Rompre et al, 2010;Li et al, 2013a,b). In addition, the associated microorganisms and their activities in hyperaccumulator rhizosphere soil also play a role in enhancing metal availability (Li et al, 2010;Wei and Twardowska, 2013). In addition to the microbial activities, soil bound metals can be released with the transformation of Fe/Al/Mn oxides when there is a shift in soil redox conditions (Husson, 2013) or decomposition of soil organic matter.…”