Organic Carbon and Eukaryotic Predation Synergistically Change Resistance and Resilience of Aquatic Microbial Communities

With dramatic global rise of urbanization, anthropogenic activities alter aquatic ecosystems in urban rivers through inputs of dissolved organic carbon (DOC) and nutrients. Microorganisms play crucial roles in global biogeochemical element cycles, providing functions to sustain microbial ecology stability. The DOC (bottom-up control) and microbial predation (top-down control) may synergistically drive the competition and evolution of aquatic microbial communities, and their resistance and resilience, of which experimental evidences remain scarce. In this study, laboratory sediment-water column experiments were employed to mimic the organic carbon-driven water blackening and odorization process in urban rivers and to elucidate impacts of DOC on the microbial ecology stability. Results showed that low DOC (25-75 mg/L TOC) and high DOC (100-150 mg/L TOC) changed the aquatic microbial community assemblies in different patterns: (1) the low DOC enriched K-selection microorganisms (e.g., bacteria and predators) with low biomass and low resilience, as well as high resistance to perturbations in changing microbial community assemblies; (2) the high DOC was associated with r-selection microorganisms with high biomass and improved resilience, together with low resistance detrimental to microbial ecology stability. Overall, this study provided new insights into impacts of DOC on aquatic microbial ecology stability, which may guide sustainable urban river management.

NanoSIMS: Microscale Quantification of Biogeochemical Activity with Large-Scale Impacts

One major objective of aquatic microbial ecology is to understand the distribution of microbial populations over space and time and in response to environmental factors. Perhaps more importantly, it is crucial to quantify how those microbial cells affect biogeochemical processes of interest, such as primary production, nitrogen cycling, or the breakdown of pollutants. One valuable approach to link microbial identity to activity is to carry out incubations with stable-isotope-labeled substrates and then quantify the isotope incorporation by individual microbial cells using nanoscale secondary ion mass spectrometry (NanoSIMS). This review summarizes recent efforts in this field, highlights novel methods, describes studies investigating rare metabolisms as well as widespread microbial activity, and hopes to provide a framework to increase the use and capabilities of NanoSIMS for microbial biogeochemical studies in the future.