COS 11-6
Effect of temperature on bacterial communities of freshwater sediment and biofilms
The Hengill Valley in Iceland provides a unique opportunity to explore the effects of temperature on freshwater ecosystems. The streams in the valley all have the same source water and are warmed indirectly by subsurface geothermal activity (water temperatures range from 5°C to 23ºC). Thus, there is little variation in water chemistry among streams and the effects of temperature can be tested without the confounding variables (e.g. wide variation iron and sulfur levels) typically observed in geothermally warmed waters. We collected sediment samples from 13 streams in the valley to determine the long-term effects of temperature on bacterial communities. We also used two experimental approaches to determine the effects of temperature on bacterial communites at shorter time scales. First, we warmed an entire stream by 3.5°C and took sediment samples monthly one year prior to warming and two years after warming. Second, we set up water channels at five temperatures (ranging from 7.5°C to 23.5°C) and let sterile tiles accumulate biofilm for 8 weeks. We extracted DNA from all samples (natural sediment, experimentally warmed sediment, and experimental biofilm) and used high-throughput DNA sequencing of 16S rRNA genes to characterize and compare bacterial communities.
Results/Conclusions
The bacterial communities of freshwater sediments were more similar within streams than among streams (Analysis of Similarity; R = 0.42, p = 0.001) and community composition varied significantly due to temperature (Mantel Test; R = 0.37, p = 0.01). Surprisingly, experimentally warming an entire stream by 3.5°C did not alter sediment bacterial communities. However, sediment communities did differ significantly based on collection date, suggesting that seasonal variation may be overwhelming any effects of the temperature increase. Temperature had a very strong effect on bacterial community composition of biofilm communities (Mantel Test; R = 0.88, p = 0.01). Overall, our results suggest that temperature can alter microbial community composition. Shifts in community composition likely alters community function, and this will be our focus in the future for this system.