Acute salt stress promotes altered assembly dynamics of nascent freshwater microbial biofilms

Freshwater ecosystems are under increasing threat of salinization due to human activity. Given the contributions of microbial communities to stream ecosystems, it is critical to understand how these communities are affected by the increasing presence of salt in the environment. We used an artificial stream system to investigate how salt concentrations representing the 95th- and 99th-percentile of concentrations observed in NE Ohio streams affect bacterial community succession and what implications this has on community-level functional capabilities. We hypothesized that the successional trajectory of community functionality (in the form of extracellular enzyme activity) and structure (via denitrification gene abundances and community 16S rRNA gene profiles) would be altered in response to increasing salt concentrations. We observed considerable structural changes in bacterial composition among treatments that corresponded with niche expansion by more salt-tolerant taxa. Increases in denitrification gene abundances and modifications to extracellular enzyme activity were also observed. These data suggest that continued salt pollution can dramatically affect community structure and has the potential to modify the functional contributions of the bacterial community to the ecosystem.