DataSheet1_Influence of Microplastics on Microbial Structure, Function, and Mechanical Properties of Stream Periphyton.docx

Periphyton is a freshwater biofilm composed of prokaryotic and eukaryotic communities that occupy rocks and sediments, forming the base of the food web and playing a key role in nutrient cycling. Given the large surface that periphyton comprises, it may also act as a sink for a diverse range of man-made pollutants, including microplastics (MP). Here we investigated the effect of 1–4 μm and 63–75 µm sized, spherical polyethylene MP with native and ultraviolet (UV)-weathered surface on developing natural stream periphyton communities over 28 days. In order to ensure proper particle exposure, we first tested MP suspension in water or in water containing either Tween 80, extracellular polymeric substances – EPS, fulvic acids, or protein. We found the extract of EPS from natural periphyton to be most suitable to create MP suspensions in preparation of exposure. Upon exposure, all tested types of MP were found to be associated with the periphyton, independent of their size and other properties. While biomass accrual and phenotypic community structure of the photoautotrophs remained unchanged, the prokaryotic and eukaryotic communities experienced a significant change in composition and relative abundances. Moreover, alpha diversity was affected in eukaryotes, but not in prokaryotes. The observed changes were more prominent in periphyton exposed to UV-treated as compared with native surface MP. Mechanical properties, as assessed by compression rheology, showed that MP-exposed periphyton had longer filamentous streamers, higher stiffness, lower force recovery and a higher viscoelasticity than control periphyton. Despite the observed structural and mechanical changes of periphyton, functional parameters (i.e., photosynthetic yield, respiration and nutrient uptake efficiencies) were not altered by MP, indicating the absence of MP toxicity, and suggesting functional redundancy in the communities. Together, our results provide further proof that periphyton is a sink for MP and demonstrate that MP can impact local microbial community composition and mechanical properties of the biofilms. Consequences of these findings might be a change in dislodgement behavior of periphyton, a propagation through the food chains and impacts on nutrient cycling and energy transfer. Hence, taking the omnipresence, high persistence and material and size diversity of MP in the aquatic environment into account, their ecological consequences need further investigation.

周丛生物（Periphyton）是一类由原核与真核群落组成的淡水生物膜，附着于岩石与沉积物表面，构成食物网的基础，并在养分循环中发挥关键作用。鉴于周丛生物拥有巨大的附着表面积，其亦可作为多种人为污染物的汇，包括微塑料（microplastics，MP）。
本研究针对粒径1–4 μm与63–75 μm、表面为原生态及紫外（ultraviolet，UV）老化的球形聚乙烯微塑料，探究其对28天培养期内自然溪流周丛生物群落的影响。
为确保微塑料颗粒能有效暴露于受试体系，本研究首先测试了以纯水、含吐温80（Tween 80）的水、胞外聚合物（extracellular polymeric substances，EPS）溶液、富里酸溶液或蛋白质溶液作为分散介质的微塑料悬浮液制备方案。研究发现，从天然周丛生物中提取的胞外聚合物是制备暴露用微塑料悬浮液的最优分散介质。
暴露实验结果显示，所有受试微塑料均能与周丛生物结合，且该结合效果不受粒径与其他属性的影响。尽管光合自养生物（photoautotrophs）的生物量积累与表型群落结构未发生显著变化，但原核与真核群落的组成及相对丰度均出现了显著改变。此外，真核生物的α多样性（alpha diversity）受到显著影响，而原核生物的α多样性则无明显变化。相较于表面为原生态的微塑料暴露组，经紫外老化的微塑料暴露组周丛生物的群落变化更为显著。
通过压缩流变学（compression rheology）测试评估的机械特性结果显示，与对照组周丛生物相比，经微塑料暴露的周丛生物具有更长的丝状絮状体、更高的刚度、更低的力恢复能力以及更高的粘弹性。尽管周丛生物出现了上述结构与机械特性的改变，但微塑料并未对其功能参数（即光合产率、呼吸作用及养分摄取效率）产生影响，这表明微塑料未表现出毒性，并提示群落存在功能冗余性。
综上，本研究结果进一步证实周丛生物可作为微塑料的汇，并证明微塑料能够影响原位微生物群落组成及生物膜的机械特性。该研究结果可能带来的影响包括：周丛生物的脱落行为发生改变、微塑料通过食物链进行传播，以及对养分循环与能量传递造成影响。因此，考虑到微塑料在水生环境中无处不在、持久性强且材质与粒径多样，其生态效应仍需开展进一步研究。