Table_2_Changes in the Drinking Water Microbiome: Effects of Water Treatments Along the Flow of Two Drinking Water Treatment Plants in a Urbanized Area, Milan (Italy).xlsx

While safe and of high quality, drinking water can host an astounding biodiversity of microorganisms, dismantling the belief of its “biological simplicity.” During the very few years, we are witnessing an exponential growth in scientific publications, exploring the ecology hidden in drinking water treatment plants (DWTPs) and drinking water distribution system (DWDS). We focused on what happens to the microbial communities from source water (groundwater) throughout the main steps of the potabilization process of a DWTP, located in an urbanized area in Northern Italy. Samples were processed by a stringent water filtration to retain even the smallest environmental bacteria and then analyzed with High-Throughput DNA Sequencing (HTS) techniques. We showed that carbon filters harbored a microbial community seeding and shaping water microbiota downstream, introducing a significant variation on incoming (groundwater) microbial community. Chlorination did not instantly affect the altered microbiota. We were also able to correctly predict (through machine learning analysis) samples belonging to groundwater (overall accuracy was 0.71), but the assignation was not reliable with carbon filter samples, which were incorrectly predicted as chlorination samples. The presence and abundance of specific microorganisms allowed us to hypothesize their role as indicators. In particular, Candidatus Adlerbacteria (Parcubacteria), together with microorganisms belonging to Alphaproteobacteria and Gammaproteobacteria, characterized treated water, but not raw water. An exception, confirming our hypothesis, is given by the samples downstream the filters renewal, which had a composition resembling groundwater. Volatility analysis illustrated how carbon filters represented an ecosystem that is stable over time, probably bearing the environmental conditions that promote the survival and growth of this peculiar microbial community.

尽管饮用水安全且品质优良，但其蕴含的微生物多样性却远超预期，彻底打破了人们认为饮用水“生物学层面较为简单”的固有认知。近年间，围绕饮用水处理厂（drinking water treatment plants, DWTP）与饮用水分配系统（drinking water distribution system, DWDS）中隐匿的微生物生态的科学研究呈指数级增长态势。本研究聚焦意大利北部某城市化区域内一座饮用水处理厂的净水全流程，追踪原水（地下水）中的微生物群落随各主要处理环节的变化情况。研究人员采用严苛的水样过滤工艺，截留哪怕是体型最小的环境细菌，随后通过高通量DNA测序（High-Throughput DNA Sequencing, HTS）技术完成样本分析。研究结果表明，活性炭滤池内定植的微生物群落会对下游水体的微生物群构成施加定植与塑造作用，使进水（地下水）的微生物群落发生显著改变。氯化消毒并未立即对已发生改变的微生物群落产生影响。此外，通过机器学习分析，研究人员可准确区分出原水（地下水）样本（整体准确率达0.71），但却无法可靠区分活性炭滤池样本——此类样本常被误判为氯化消毒后的样本。特定微生物的存在与丰度特征可帮助我们推测其作为指示物种的潜在功能。具体而言，候选Adlerbacteria属（Candidatus Adlerbacteria, Parcubacteria），以及属于α-变形菌纲（Alphaproteobacteria）和γ-变形菌纲（Gammaproteobacteria）的微生物，共同构成了处理后饮用水的菌群特征，而原水则无此特征。滤池更新后下游采集的样本是印证本研究假说的特例：此类样本的菌群组成与原水地下水高度相似。波动分析结果显示，活性炭滤池是一个长期保持稳定的微生态系统，其所处的环境条件大概率可促进这类特殊微生物群落的存活与增殖。