History Strongly Affects Bacterial Community Re-Assembly and Ecosystem Function Under a Common Environmental Selection Regime

Background/Question/Methods

Microbes profoundly shape the ecosystems of our planet, yet we still lack a clear understanding of how their community structures and functions impact vital processes. Here, we use pitcher plant microcosms to investigate if community composition and ecosystem function converge over time in a serial passage experiment. The cup-shaped leaves of carnivorous pitcher plants house entire, small ecosystems (or microcosms) that are ideal for biological study: each one is similar but independent. We collected microcosm fluids from 10 different pitchers growing in the wild, and brought them into the lab where we grew them on sterilized insect material and conducted serial passages over 60 days under common conditions. Throughout the time series, we measured community and gene composition via amplicon and shotgun metagenomic sequencing, as well as functional calculations of CO 2  production, growth activity on different substrates, and chitinase activity.

Results/Conclusions

We found convergence in CO 2  production over time; however, robust differences remained in the activity of three different chitinases and in community compositions. Our results suggest that while the overall metabolic rates stabilized across the microcosms, the different pitcher communities were consuming different compounds. A common environmental selection regime is not sufficient for generating functional convergence in bacterial communities over the measured time period, and historical effects remain significant.