U.S. Department of Energy

Pacific Northwest National Laboratory

Assembly of Microbial Communities Affects Biogeochemistry

A conceptual model in which stochastic assembly processes decrease biogeochemical function. Purple organisms represent well-adapted species, yellow and green organisms represent less adapted species. (A) Community of well-adapted species, resulting in enhanced biogeochemical function. (B) Community with increased abundance of maladapted (non-native) organisms, resulting in lower biogeochemical function. (C) Community with high rate of dispersal (large portion of species are maladapted), resulting in the lowest rates of biogeochemical function.

The Science

Microbial communities are like our own societies. In their natural environments, where they’re comfortable and acclimated, both microbes and humans tend to thrive. They know how to navigate their surroundings, how to survive, and they concentrate their energy on being productive. 

When dispersed to an unfamiliar environment, organisms are naturally maladapted to their surroundings. And in communities with more organisms arriving through dispersal, research indicates there’s a lower rate of functioning. This concept, detailed in a new paper by PNNL researchers Emily Graham and James Stegen, brings us a step closer to understanding how a microbial community functions based on how it was assembled. 

The Impact

Microbial communities have a profound impact on biogeochemical processes, which transform chemical nutrients as they circulate through biological and physical worlds. By increasing our understanding of how microbial communities function, we can develop models that predict important things such as the rate of nutrient cycling in a given area, during a given time of year.

Summary

Microbial communities are assembled by deterministic (selection) and stochastic (dispersal) processes. The relative influence of these two process types is believed to alter how microbial communities affect biogeochemical function. But recent attempts to link microbial communities and environmental biogeochemistry have yielded mixed results.

In this study, Graham and Stegen proposed a new conceptualization of microbial-biogeochemical relationships and created an ecological simulation model to demonstrate that microbial dispersal decreases biogeochemical function. Simply put, microbes that disperse into a community aren’t as productive as ones that were selected to live within that environment.

In a community of microbes selected to live in that environment, the microbes were well-adapted to their environment and productivity was high. But when microbes were introduced to the community via dispersal, productivity decreased, even as diversity increased.

In communities comprised mostly of microbes arriving via dispersal, productivity decreased significantly. Stegen and Graham propose that this effect is pronounced in natural settings in which dispersing microbes use more energy for survival than for catalyzing biogeochemical processes. This indicates that community structure and function are linked via ecological assembly processes that are influenced by microbial adaptation to local conditions.

The next step, say researchers, is incorporating assembly processes into emerging model frameworks that explicitly represent microbes and that mechanistically represent biogeochemical reactions. Specifically, the researchers plan to incorporate this framework into ongoing efforts by the PNNL SBR SFA team using a reactive transport model (PFLOTRAN) applied across a broad range of spatial and temporal scales.

Funding

This research was supported by the U.S. Department of Energy’s Office of Biological and Environmental Research (BER), as part of Subsurface Biogeochemical Research Program’s Scientific Focus Area (SFA) at the Pacific Northwest National Laboratory (PNNL). This research was performed using Institutional Computing at PNNL. 

Publications

E. Graham, and J. Stegen, “Dispersal-Based Microbial Community Assembly Decreases Biogeochemical Function.” Processes2017, 5(4), 65; doi:10.3390/pr5040065.

Related Links

https://www.pnnl.gov/science/highlights/highlight.asp?groupid=753&id=4589

https://phys.org/news/2016-12-microbial-hyporheic-zone.html

http://sbrsfa.pnnl.gov/docs/highlights/Highlight_Stegen_Microbial_Communities_11282016.pdf

http://sbrsfa.pnnl.gov/docs/highlights/Highlight_Stegen_10-8-2015.pdf

http://sbrsfa.pnnl.gov/docs/highlights/Highlight_Stegen_et_al_2015.pdf

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