Data_Sheet_2_Metatranscriptomic Insights Into the Response of River Biofilm Communities to Ionic and Nano-Zinc Oxide Exposures.xlsx

Manufactured Zn oxide nanoparticle (ZnO-NP) are extensively used world-wide in personal care and industrial products and are important contaminants of aquatic environments. To understand the overall impact of ZnO-NP contamination on aquatic ecosystems, investigation of their toxicity on aquatic biofilms is of particular consequence, given biofilms are known sinks for NP contaminants. In order to assess alterations in the functional activity of river microbial biofilm communities as a result of environmentally-relevant ZnO-NP exposure, biofilms were exposed to ionic zinc salt or ZnOPs that were uncoated (hydrophilic), coated with silane (hydrophobic) or stearic acid (lipophilic), at a total concentration of 188 μg l–1 Zn. ICP-MS analyses of biofilms indicated ZnO-NP concentrated in the biofilms, with hydrophilic, hydrophobic, and lipophilic treatments reaching 0.310, 0.250, and 0.220 μg Zn cm–2 of biofilm, respectively, while scanning transmission X-ray microspectroscopy (STXM) analyses of biofilms confirmed that Zn was extensively- and differentially-sorbed to biofilm material. Microbial community composition, based on taxonomic affiliation of mRNA sequences and enumeration of protozoa and micrometazoa, was not affected by these treatments, and the total transcriptional response of biofilms to all experimental exposures was not indicative of a global toxic-response, as cellular processes involved in general cell maintenance and housekeeping were abundantly transcribed. Transcripts related to major biological processes, including photosynthesis, energy metabolism, nitrogen metabolism, lipid metabolism, membrane transport, antibiotic resistance and xenobiotic degradation, were differentially expressed in Zn-exposures relative to controls. Notably, transcripts involved in nitrogen fixation and photosynthesis were decreased in abundance in response to Zn-exposure, while transcripts related to lipid degradation and motility-chemotaxis were increased, suggesting a potential role of Zn in biofilm dissolution. ZnO-NP and ionic Zn exposures elicited generally overlapping transcriptional responses, however hydrophilic and hydrophobic ZnO-NPs induced a more distinct effect than that of lipophilic ZnO-NPs, which had an effect similar to that of low ionic Zn exposure. While the physical coating of ZnO-NP may not induce specific toxicity observable at a community level, alteration of ecologically important processes of photosynthesis and nitrogen cycling are an important potential consequence of exposure to ionic Zn and Zn oxides.

人工合成的氧化锌纳米颗粒（ZnO-NP）目前已在全球范围内的个人护理与工业产品中广泛应用，同时也是水生环境中的重要污染物。鉴于生物膜是纳米颗粒（NP）污染物的已知沉降库，因此在阐明ZnO-NP污染对水生生态系统的整体影响时，探究其对水生生物膜的毒性具有尤为重要的意义。为评估在环境相关浓度的ZnO-NP暴露下，河流微生物生物膜群落的功能活性变化，研究人员将生物膜分别暴露于总锌浓度为188 μg·L⁻¹的离子锌盐，以及未包膜（亲水型）、硅烷包膜（疏水型）或硬脂酸包膜（亲脂型）的ZnOPs。电感耦合等离子体质谱法（ICP-MS）对生物膜的分析结果显示，ZnO-NP在生物膜中发生富集：亲水型、疏水型和亲脂型处理组的锌负载量分别达到0.310、0.250和0.220 μg Zn·cm⁻²生物膜；而扫描透射X射线显微光谱法（STXM）分析进一步证实，锌被广泛且差异化地吸附于生物膜基质中。基于mRNA序列的分类学归属以及原生动物和微型后生动物的计数结果显示，各组微生物群落组成均未受上述处理的影响；同时，生物膜对所有实验暴露的整体转录应答并未呈现全局性毒性应答特征，因为参与细胞基础维持与持家功能的细胞过程均被大量转录。与光合作用、能量代谢、氮代谢、脂质代谢、膜转运、抗生素抗性以及异生物质降解等核心生物学过程相关的转录本，在锌暴露组与对照组间呈现差异化表达。值得注意的是，响应锌暴露后，固氮与光合作用相关的转录本丰度出现下调，而脂质降解以及运动-趋化相关的转录本丰度则有所上调，这表明锌可能在生物膜解离过程中发挥潜在作用。ZnO-NP与离子锌暴露总体上引发了相似的转录应答，但亲水型与疏水型ZnO-NPs所诱导的效应相较于亲脂型ZnO-NPs更为显著；而亲脂型ZnO-NPs的效应与低浓度离子锌暴露相似。尽管ZnO-NP的物理包膜在群落水平上未必会诱导可观测的特异性毒性，但离子锌与氧化锌暴露仍可能对具有重要生态意义的光合作用与氮循环过程造成改变，这是此类暴露的重要潜在生态后果。