拉恩氏菌LRP3诱导形成碱式磷酸锌沉淀及其在Zn污染土壤修复中的作用

采用批式和土壤培养实验考察拉恩氏菌LRP3对Zn的磷酸盐矿物诱导及其在Zn污染土壤修复中的作用,并进行X射线衍射、扫描电子显微镜、能谱及Fourier变换红外光谱分析.结果表明,菌株LRP3对Zn^(2+)的最大耐受质量浓度为120mg/L;对溶液中Zn^(2+)的去除率为菌体细胞(97.4%)>发酵液(88.2%)>无菌发酵液(81.6%);菌株LRP3的发酵液可通过生物矿化作用诱导形成结晶良好的立方体状Zn_2(OH)PO_3矿物晶体;菌株LRP3的发酵液加入土壤后可快速降低DTPA-Zn的质量比,培养5d后DTPA-Zn的质量比平均下降78.4%,培养6d后土壤中Zn的弱酸提取态和可氧化态的质量比分别下降72.5%和56.2%,可还原态和残渣态的质量比分别增加85.1%和14.8%.因此,菌株LRP3对Zn^(2+)具有较强的抗性和吸附能力,可通过降解植酸释放磷酸根,进一步诱导形成碱式磷酸锌矿物晶体,从而降低土壤中Zn的生物有效性,可用于Zn污染土壤的绿色可持续修复.

A Comparative Toxicity Study of TiO2 Nanoparticles in Suspension and Adherent Culture Under the Dark Condition

The present study focused on the different acute toxicity of TiO2 nanoparticles（TiO2 NPs） towards the bacteria in suspension culture and adherent culture under the dark conditions. The study investigated the bacteria toxicity with TiO2 NPs at different concentrations（1-2000 mg/L）, sizes（10 nm, 35 nm） and specific surface areas in unit volume solution（0-224 m^2/L） characterized by the cell viability, extracellular polymeric substances（EPS） release and biofilm formation. The bacteria in adherent culture was found to be more resistant against the toxicity of TiO2 NPs compared to that in suspension culture. An NP dose and surface area dependent（rather than the size） bacterial viability was observed in suspension culture, specifically the surface area positively correlated with the toxicity of TiO2 NPs. The size of TiO2 NPs, however, played a more critical role in toxicity of TiO2 NPs in adherent culture. Therefore, the surface area dependent toxicity of TiO2 NPs is a comprehensive parameter describing the dose and size dependent toxicity of TiO2 NPs. The electron microscopic（SEM, TEM, EDX） observations suggested the EPS release and biofilm formation, during aggregation of TiO2 NPs on the bacteria after 12 h cultivation in adherent culture under the dark condition. A possible toxic mechanism could be that ＂effective surface areas＂ that directly contact with the bacterial membrane greatly contributed to the toxicity of TiO2 NPs in both suspension culture and adherent culture. Therefore, as for the possible resistance mechanism, EPS secretion and subsequent biofilm formation may protect the bacteria against the toxicity of TiO2 NPs.

氧化木糖无色杆菌(Achromobacte rxylosoxidans)LAX2对Cu、Pb和Cd复合污染土壤的生物矿化修复研究

我国土壤重金属复合污染较为突出,是目前亟待解决的土壤环境问题之一.本文研究了一株氧化木糖无色杆菌LAX2对Cu、Pb和Cd共存体系的生物矿化作用及其复合污染土壤的矿化修复作用.结果表明,菌株LAX2的发酵液、无菌发酵液和菌体细胞对3种重金属的去除能力大小顺序均为Pb^(2+)>Cd^(2+)>Cu^(2+).X-射线衍射、扫描电镜、红外光谱和能谱分析表明,3种重金属共存时菌株LAX2发酵液可诱导形成PbCO_3和CdCO_3晶体,而Cu不能单独成矿,混合矿物晶体呈长杆状.菌株LAX2发酵液能够明显降低黑钙土和白浆土中Cu、Pb和Cd的有效态含量,矿化修复30 d后,黑钙土中Cu、Pb、Cd的有效态含量分别降低了48.0%、71.4%、62.8%,白浆土中Cu、Pb、Cd的有效态含量分别降低了42.0%、63.2%、53.6%;碳酸盐结合态和铁锰氧化物结合态含量明显增加,可交换态和有机物结合态含量明显降低.矿化修复后的土壤中重金属的浸出毒性随修复时间的增长而降低,黑钙土中Cu、Pb、Cd浸出量分别降低了90.3%、93.2%、92.8%,白浆土中Cu、Pb、Cd浸出量分别降低了82.5%、86.1%、84.3%.以上结果说明,菌株LAX2可通过碳酸盐矿化作用固定土壤中的复合重金属,且在相同条件下对黑钙土的修复效果好于白浆土.