PS 78-195
Dissecting microbial habitats in stratified lakes: Evidence of deterministic changes in free-living and particle-associated bacterial community composition across a productivity gradient

Friday, August 15, 2014
Exhibit Hall, Sacramento Convention Center
Marian L. Schmidt, Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI
Vincent J. Denef, Ecology and Evolutionary Biology, University of Michigan, Ann Arbor, MI

In freshwater systems bacteria dominate carbon and nutrient processing and can influence regional and global elemental cycles.  In particular, particles are hotspots of microbial activity and organic matter mineralization in the water column of lakes, however, particles are often left out of microbial ecology studies.  In addition, increased productivity in lakes influences the composition and ecology of lake bacterial communities.  To date, no studies have focused on how these spatial (particles) and environmental (productivity) changes work in combination to influence bacterial community composition (BCC).   We characterized the BCC of 10 lakes across a productivity gradient, which included three eutrophic (high productivity), three mesotrophic (medium productivity), and four oligotrophic (low productivity) lakes.  At each lake, we collected duplicate samples of the “particle-associated” and “free-living” bacterial community from the epilimnion and hypolimnion.  Next, BCC was inferred using high throughput tag sequencing of the 16S rRNA gene followed by analysis of the sequences using the Mothur program and multivariate statistics in R.


Oligotrophic BCC separates more strongly by particle-associated and free-living than by the depth of where the sample was taken (i.e. epilimnion or hypolimnion).  In the eutrophic and mesotrophic lakes BCC separated more strongly by epilimnion and hypolimnion rather than by particle-associated and free-living.  In terms of taxonomic groups, Armatimonadetes and Planctomycetes were more abundant in oligotrophic lakes while Chlorobi, Chloroflexi, Firmicutes, and Lentisphaerae increased with productivity and were therefore more abundant in mesotrophic and eutrophic lakes.  As with other studies, our results support that Actinobacteria prefer a free-living lifestyle while Planctomycetes prefer a particle-associated lifestyle.  Many taxa were specific to eutrophic and mesotrophic bottom waters, including Chlorobi and Lentisphaerae in the free-living fraction, Chloroflexi in the particle associated fraction, and Firmicutes in both free-living and particle-associated fractions.  These results help to reveal the spatial and environmental distributions of these taxonomic groups, which will help us to hone in on their ecological role in nutrient processing in lakes.