Groundwater biofilms

Stormwater infiltration systems (SIS) have been developed to limit surface runoff and urban flooding. The impacts of such practices on the ecological and biological quality of groundwater ecosystems remain poorly studied due to the lack of efficient methodologies to assess microbial qualities of aquifers. In the present study, a method based on the incubation of artificial substrates (clay beads) is presented to evaluate microbial biomass, microbial activity and bacterial community structures. Three urban water types (stormwater surface runoffs, and SIS-impacted or not impacted groundwaters) collected from 6 sites were considered. Total proteins, dehydrogenase and hydrolytic activities were used to monitor biofilm development on clay beads. Analyses based on next generation sequencing (NGS) of partial rrs (16S rRNA) PCR products (V5-V6) were used to compare operating taxonomic units (OTUs, defined as groups of DNA sequences sharing more than 97% identity) of 10 day-old clay beads biofilms with those of waters collected from the same sampling point. Clay beads biofilm biomass and enzymatic activities were found indicative of biodegradable dissolved organic carbon transfers from the surface to the SIS-impacted groundwaters. Biofilms developing on clay beads also allowed determining the impact of SIS on groundwater bacterial genetic community structures. Although rrs OTU profiles of clay bead biofilms did not perfectly match the diversity of the waters collected from the same sampling points, they were found to have captured the most abundant OTUs. They also captured OTUs not detected in these waters, suggesting exposure prior the sampling time and demonstrating the integrative character of this approach. Monitoring biofilms developing on clay beads allowed a tracking of bacterial genera containing species representing health concerns such as Bordetella and Legionella, and genera involved in key functional processes such as Nitrospira involved in nitrification and Azospirillum involved nitrogen-fixation. Clay beads were found efficient germcatchers that could be used to investigate the incidence of SIS management practices on the connected aquifer microbiological state.雨水渗透系统（Stormwater Infiltration Systems，SIS）旨在抑制地表径流与城市内涝。由于缺乏可有效评估含水层微生物特性的方法，此类设施对地下水生态系统生态与生物质量的影响仍鲜有研究。本研究提出一种基于人工基质（陶粒，clay beads）培养的方法，用于评估微生物生物量、微生物活性与细菌群落结构。研究选取了6个采样点采集的三类城市水体样本：雨水地表径流、受SIS影响及未受SIS影响的地下水。通过总蛋白含量、脱氢酶活性与水解酶活性，可监测陶粒表面生物膜的生长情况。本研究通过对部分rrs（16S rRNA）PCR产物（V5-V6区）进行高通量测序（Next Generation Sequencing，NGS）分析，将培养10天的陶粒生物膜的操作分类单元（Operating Taxonomic Units，OTUs，定义为序列相似度≥97%的DNA序列簇）与同采样点采集的水体样本进行对比。研究发现，陶粒生物膜的生物量与酶活性可反映地表径流向受SIS影响的地下水传递的可生物降解溶解有机碳。陶粒表面生长的生物膜还可用于评估SIS对地下水细菌遗传群落结构的影响。尽管陶粒生物膜的rrs OTU谱与同采样点水体的微生物多样性并非完全匹配，但研究发现其已覆盖了丰度最高的OTUs。此外，该方法还能检测到水体样本中未检出的OTUs，表明陶粒在采样前已暴露于相关微生物，同时证明了该方法的整合性特点。通过监测陶粒表面生长的生物膜，可追踪携带潜在致病物种的细菌属（如博德特菌属（Bordetella）与军团菌属（Legionella）），以及参与关键功能过程的细菌属（如参与硝化作用的硝化螺旋菌属（Nitrospira）与参与固氮作用的固氮螺菌属（Azospirillum））。研究表明，陶粒是高效的微生物捕获载体，可用于探究SIS运维措施对关联含水层微生物状态的影响。