Use of local dissimilatory metal reducing bacteria Shewanella sp. KR12 to degrade four herbicides

• Main Authors: Yu-Hsin Hsiung, 熊禹昕
• Other Authors: Jui-Hung Yen
• Format: Others
• Language: zh-TW
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/95027840369869650685

碩士 === 國立臺灣大學 === 農業化學研究所 === 105 === The genus Shewanella is a group of metal reducing facultative anaerobes which are noted for their outstanding ability to utilize a wide range of materials including various metal ions as electron acceptors in anaerobic respiration processes, which allow them to couple the degradation of organic pollutants to the removal of heavy metals in environment. Hence, Shewanella bacteria are considered rising stars in the bioremediation field. In particular, several strains have been found to form metallic bio-nanoparticles extracellularly by bioreduction of metal ions. Recently, the concept of “green chemistry” is becoming more significant to environmental nanotechnology development. In the present study, a local dissimilatory metal reducing bacterium Shewanella sp. KR12 was used to biosynthesis zinc sulfide (ZnS) nanoparticles, whereby the immobilization of zinc ions from zinc sulfate solution by bacterial sulfur reduction. Characterization of nanoparticles were analyzed using transmission electron microscopy (TEM), energy dispersive spectrometer (EDS), cold field emission scanning electron microscopy (FESEM), X-ray powfer diffractometer (XRD) and ultraviolet-visible spectroscopy (UV-Vis). Furthermore, photocatalytic properties of ZnS nanoparticles and organic compounds biodegrading ability of Shewanella sp. KR12 were both investigated for application as remediation materials for degradation of four most frequently detected herbicides in river water in Taiwan, such as ametryn, diuron, oxadiazon and thiobencarb. Our findings revealed that the hydrogen sulfide (H2S) possibly produced through cysteine degradation by Shewanella sp. KR12 then dissociated into S2- to form precipitates with Zn2+ as extracellular ZnS nanoparticles. The nanoparticles were observed to have well dispersion in bacterial surface, periplasm and liquid medium, with a spherical shape and an average diameter of 10 nm. UV-Vis spectrum indicated ZnS bio-nanoparticles had a strong absorption between 290 and 300 nm. Further studies demonstrated biogenic ZnS nanoparticles formed by Shewanella sp. KR12 showed good catalytic performance toward the degradation of diuron and oxadiazon in aqueous solution under UV irradiation. In addition, strain KR12 exhibits degrading ability toward oxadiazon and thiobencarb in direct biodegradation test of herbicides under anaerobic condition. Conclusively, this approach of coupling biosynthesis of nanoparticles with heavy metal removal may offer a potential material for photocatalytic water treatment.