Toxicology and bioremediation studies on heavy metals and phenol using Pseudomonas aeruginosa and Ralstonia taiwanensis

• Main Authors: Chih-Hui Wu, 吳智輝
• Other Authors: Jo-Shu Chang
• Format: Others
• Language: zh-TW
• Published: 2004
• Online Access: http://ndltd.ncl.edu.tw/handle/40131940276518817941

碩士 === 國立成功大學 === 化學工程學系碩博士班 === 92 === In this study, we investigated the toxic effect of organic and inorganic pollutants on the microorganisms used for bioremediation. Pseudomonas aeruginosa PU21 was chosen as a model system for toxic analysis of Co, Mn, Cd, and Zn. It is discovered that the metals tested had different toxic effect on PU21 in different buffer medium. With LB/citric acid-phosphate buffer (CAPBS) medium, the sequence of toxic effect was Co > Mn ~ Zn > Cd. With LB/phosphate buffer saline (PBS) medium, the toxicity sequence became Co > Cd > Mn. The metals exhibited higher toxic effect in PBS than in CAPBS, probably due to the chelating property of citric acid in CAPBS. Citric acid may form complexes with metal ions to reduce the availability of free metal ions and thereby decreased their toxicity. This result suggests that the chelating agents may be supplemented into the metal contaminated environment to decrease the toxic effect on microorganisms for higher bioremediation efficiency. A novel root nodule bacterium, Ralstonia taiwanensis, originally isolated from Mimosa sp. in southern Taiwan was investigated for its ability to remediate organic and inorganic contaminants. Phenol was selected as target pollutant to examine the biodegradative ability of the R. taiwanensis strain. The dependence of phenol degradation rate on phenol concentration can be described by Haldane model with a low KS (the apparent half-saturation constant) of 5.46 μM and an extremely high KSI (the apparent inhibition constant) of 9075 μM. The optimal phenol degradation rate was 61 μmol/min/g cell, which occurred at a phenol concentration of 228 μM. The Results from kinetic analysis suggest that R. taiwanensis is a dominant bacterial for phenol degradation. For bioremediation of inorganic contaminants by R. taiwanensis, the efficiency of adsorption of Pb, Cu, and Cd by the biomass of R. taiwanensis was investigated. The dependence of adsorption capacity on metal concentration can be described by Langmuir isotherm model. The maximum uptake of the biomass were 50.1 mg Pb/g dry cell, 19.0 mg Cu/g dry cell, and 19.6 mg Cd/g dry cell. Combined system of Mimosa sp. and its root nodule R. taiwanensis was tested for bioremediation. It is proposed that the symbiotic relationship between rhizobia R. taiwanensis and its host plant Mimosa sp. may be beneficial for phenol degradation and metal removal. For phenol degradation, Mimosa sp with R. taiwanensis root nodules was shown to be able to degrade phenol efficiently, whereas Mimisa sp without root nodules had not phenol degradation capability. This suggests that R. taiwanensis can help Mimosa sp to decompose the organic compound. For the treatment of metal ions, Langmuir isotherm was also used to simulate the relationship between adsorption capacity (mg metal/g dry root) and metal concentration. The adsorption capacity decreased in the order of Mimosa sp with R. taiwanensis root nodules > Mimosa sp without root nodules > R. taiwanensis alone. The results indicate that root nodules really increased the efficiency of phytoremediation of the organic and the inorganic pollutants.