Bacterial communities in trace metal contaminated lake sediments are dominated by endospore-forming bacteria

Abstract

Lake sediments in areas close to the outlet of wastewater treatment plants are sinks for pollutants. Bacterial communities in sediments are likely affected by the released effluents, but in turn they might modify the distribution and bioavailability of pollutants. On the shore of Lake Geneva, Switzerland, wastewater from the City of Lausanne is treated and discharged into the lake via an outlet pipe in the Vidy Bay. The objectives of this study were to assess (1) the impact of the treated wastewater release on the bacterial communities in the Vidy Bay sediments and (2) the potential link between bacterial communities and trace metal sediment content. Bacterial community composition and abundance were assessed in sediments collected in three areas with different levels of contamination. The main factors affecting bacterial communities were inferred by linking biological data with chemical analyses on these sediments. Near to the outlet pipe, large quantities of bacterial cells were detected in the three upper most cm (3.2 9 10 9 cells assessed by microscopy and 1.7 9 10 10 copies of the 16S rRNA gene assessed by quantitative PCR, per gram of wet sediment), and the dominant bacterial groups were those typically found in activated sludge (e.g. Acidovorax defluivii and Hydrogenophaga caeni). Three samples in an area further away from the outlet and one sample close to it were characterized by 50 % of endospore-forming Firmicutes (Clostridium spp.) and a clear enrichment in trace metal content. These results highlight the potential role of endospore-forming Firmicutes on transport and deposition of trace metals in sediments.

Effect of Pollution on Aquatic Microbial Diversity

“…Among other groups, sulfate-and iron-reducing clades belonging to Deltaproteobacteria were also abundant in the contaminated sediments. More recently, Sauvain and co-workers conducted microbial community profiling from similar locations in Lake Geneva and observed a high abundance of endospore-forming Firmicutes, closely related to Clostridium (Sauvain et al 2014). This discovery has demonstrated the potential of spore-forming Firmicutes to be used as proxies for assessing stress conditions in lake environments ).…”

Influence of a wastewater treatment plant on mercury contamination and sediment characteristics in Vidy Bay (Lake Geneva, Switzerland)

“…All p values were found to be [0.05 (Table 4), which suggests that there was no statistical difference between sediment type and logK d , MMHg PW , MMHg PW /THg PW ratio, nonfiltered THg OW and filtered MMHg OW concentrations. Therefore, at the studied scale, it appeared that the strong differences in sediment surfaces were essentially due to redox variations at the sediment surface and the presence or absence of a bacterial mat (Sauvain et al 2013, this issue). These differences seemed to have no direct effect on mercury transformation processes in the sediment.…”

Into the abyss of Lake Geneva: the elemo interdisciplinary field investigation using the MIR submersibles

“…Differences in trace-metal speciation in the sediment and overlying water were found to have a higher correlation with bacterial community, abundance, type, and activity rather than with the distance from the WWTP sewage outlet . Their results highlight the potential role of endospore-forming Firmicutes for the transport and sediment deposition of trace metals released from effluents (Sauvain et al 2014). Observed increases in dissolved metal concentrations in the interstitial water were attributed to organic matter mineralization.…”

“…The scientists' ability to visually and precisely select coring sites at close range was pivotal to the success of these field measurements. Sauvain et al (2014) used DNA recovery techniques and found large quantities of bacterial groups, identified as those typical for activated sludge in sediments near the WWTP outlet. Trace-metal analysis and speciation were performed at the sediment-water interface within Vidy Bay.…”