以異化金屬還原菌Shewanella sp. NC1生物合成奈米硫化鋅及其在光催化降解三種殺菌劑中之應用

Abstract

Shewanella 是一種能夠異化金屬還原的兼性厭氧菌。 Shewanella 可生物合成奈米等級之金屬降解有機污染物，並使用多種細胞外電子接受者完成無氧呼吸，可同時解決環境中重金屬及有機物的問題。故Shewanella於環境復育是相當具有潛力。 本研究之分離株 Shewanella sp. NC1篩選自嘉義縣八掌溪之底泥中，利用BLAST 分析該菌群之16s rRNA及 gyrB 基因序列，推測分離株為一新菌種。該菌群可生物合成奈米等級之零價鈀、硫化鐵及硫化鋅，其所生成之硫化鋅為最經濟之光催化降解奈米顆粒。利用穿透式電子顯微鏡 (transmission electron microscopy) 、X光繞射儀 (X-ray diffractometer) 及全波長掃描式分光光度計 (UV-Vis scanning spectrophotometer) 進行奈米硫化鋅之特性分析。結果顯示NC1可將奈米等級之硫化鋅均勻分布於菌體表面，且於紫外光290 nm下具有特定之吸收峰。故利用NC1嘗試降解常見於臺灣南部河川中三種殺菌劑亞托敏 (azoxystrobin) 、待克利 (difenoconazole) 及菲克利 (hexaconazole) ，試驗結果顯示NC1所生成之奈米硫化鋅於20小時光催化降解試驗皆可降解該三種殺菌劑。本研究利用較環境友善之方式生物合成奈米硫化鋅降解河川中之殺菌劑，可進一步用於改善汙水處理。

Shewanella is a genus of facultative anaerobic bacteria capable of dissimilatory metal reduction. Known for their respiratory prowess, Shewanella bacteria can utilize a wide variety of substances as extracellular electron acceptors to complete anaerobic respiration. Furthermore, Shewanella’s metal reducing ability allows it to biofabricate certain metal nanoparticles that could be used to degrade organic pollutants, coupling the remediation of heavy metals with organic pollutants. Hence, Shewanella bacteria have numerous applications in the area of environmental remediation. In this study, a novel dissimilatory metal reducing bacterium was isolated from a river in Southern Taiwan. BLAST analysis of the bacterium’s 16s rRNA and gyrB genes revealed that it may be a new species of the Shewanella genus, and was subsequently characterized and labeled Shewanella sp. NC1. The bacterium was then used to produce Palladium (Pd), iron sulfide (FeS), and zinc sulfide (ZnS) nanoparticles, of which ZnS exhibits photocatalytic ability under irradiation of UV light, and is more cost effective. Thus, the biofabricated ZnS was characterized with transmission electron microscopy (TEM), X-ray diffraction (XRD), and UV-Vis scanning spectrophotometry. Results show that the biofabricated ZnS particles were well-dispersed on the surface of NC1 in the nanometer scale. Furthermore, the ZnS particles exhibited good UV absorbance under 290 nm. The organic pollutant degradation capability of the biofabricated ZnS nanoparticles, along with NC1, were then investigated on three fungicides that were frequently detected in eight major rivers of Southern Taiwan. Results of 72 h incubation treatments of NC1 with the fungicide, azoxystrobin, difenoconazole, or hexaconazole, showed that NC1 did not significantly decrease the concentration of the fungicides. On the other hand, ZnS nanoparticles biofabricated and supported by NC1 showed good photocatalytic removal of fungicides in 20 h experiments under UVC irradiation. This study offers an environmentally friendly approach to synthesize nanoparticles with pollutant degradation capabilities, which could be applied for water treatment with further optimization.