Impact of Temperature, Nutrients and Heavy Metals on Bacterial Diversity and Ecosystem Functioning Studied by Freshwater Microcosms and High-Throughput DNA Sequencing.

Microbial communities are fundamental components in freshwater, and community shifts in ecosystem structure are indicative of changing environmental conditions. This study aimed at investigating the influence of key environmental parameters on bacterial diversity and ecosystem functioning (i.e. organic matter breakdown) in laboratory freshwater microcosms. The effects of varying temperatures (5, 20 and 35 °C), nutrients (representing low, medium and high urbanization) and heavy metals Copper (Cu) and Zinc (Zn) on bacterial diversity and organic matter (OM) breakdown were studied by using leaf bags and capsules filled with polycaprolactonediol-2000 (PCP-2000), respectively. The leaf-associated bacterial diversity was determined by next-generation sequencing of SSU rRNA gene amplicons. The results showed that bacterial diversity increased at high temperature (35 °C) with more operational taxonomic units (OTUs) as compared to medium (20 °C) or low (5 °C) temperatures, whereas nutrient variation had fewer effects on the bacterial community structure. In contrast, the presence of heavy metals, especially high concentrations (100 μM) of Cu, reduced the number of OTUs in the leaf-associated bacterial community. The higher temperatures and nutrient levels accelerated PCP-2000 breakdown rate, but this was impeded by a high concentration (100 μM) of Cu in the short term, though no effect of Zn on breakdown rate was observed. The overall results indicate that temperature and variated heavy metals are among the key factors that affect bacterial diversity and ecosystem functioning in freshwater systems.