Microbial ecology of insular systems: How do immigration rates and source community diversity influence the development of stable communities?
Franklin, Rima*,1, Mills, Aaron 1, 1 NASA Space Life Science Lab, Kennedy Space Center, FL, USA
ABSTRACT- Rules controlling the assembly of individual bacterial populations into complex microbial communities are unknown. We examined the role of one potentially important factor - the ability of the system to recruit community members from adjacent locations - in the development of stable assemblages. Microcosm experiments were conducting using long-term incubations (> 100 days) of fed-batch bioreactors containing sewage microorganisms, and different treatments were established to manipulate the insularity of the system. To mimic a "closed" habitat (i.e., isolated from potential recruitment of new community members), microcosms were maintained using aseptic technique and sterile artificial sewage as the growth medium. In the "open" communities, the growth medium was supplemented daily with a small amount of raw sewage (10 ml) to provide a continuous source of new potential diversity. Weekly monitoring of several microbial community properties (total abundance / biomass, productivity, community structure and diversity) and environmental parameters (pH and nutrient concentrations) demonstrated that insularity significantly influenced the development of the communities. Specifically, the open community was more stable and better able to adjust to changing environmental conditions. After three weeks, the open communities were relatively stable, while variability over time and among replicates was much greater in the closed system. Each community's resistance to environmental (temperature change) and biological (starvation) stresses was monitored, and experiments were conducted to determine whether the effect of isolation changed depending on the microbial communities' initial diversity or composition. The results of this work suggest that immigration and recruitment may be important in determining community structure, function, and stability - even in established systems with relatively high diversity, and has important implications for extrapolation of the results of laboratory studies to natural environments. Efforts to predict the consequences of habitat disruption on microbial communities, and the ecosystem functions they perform, may be more successful if the potential for interaction among neighboring communities is considered.
Key words: microbial communities, stability, diversity, insularity
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