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Microorganisms will be an integral part of biologically based waste processing systems used for water purification or nutrient recycling on long-term space missions planned by the National Aeronautics and Space Administration. In this study, the function and stability of microbial inocula of different diversities were evaluated after inoculation into plant-based waste processing systems. The microbial inocula were from a constructed community of plant rhizosphere-associated bacteria and a complexity gradient of communities derived from industrial wastewater treatment plant-activated sludge. Community stability and community function were defined as the ability of the community to resist invasion by a competitor (Pseudomonas fluorescens 5RL) and the ability to degrade surfactant, respectively. Carbon source utilization was evaluated by measuring surfactant degradation and through Biolog and BD oxygen biosensor community level physiological profiling. Community profiles were obtained from a 16S-23S rDNA intergenic spacer region array. A wastewater treatment plant-derived community with the greatest species richness was the least susceptible to invasion and was able to degrade surfactant to a greater extent than the other complexity gradient communities. All communities resisted invasion by a competitor to a greater extent than the plant rhizosphere isolate constructed community. However, the constructed community degraded surfactant to a greater extent than any of the other communities and utilized the same number of carbon sources as many of the other communities. These results demonstrate that community function (carbon source utilization) and community stability (resistance to invasion) are a function of the structural composition of the community irrespective of species richness or functional richness.

Microbial communities in the sediment and associated with the dominant type of standing dead plant were collected from the high marsh zones of 10 sites along the eastern coast of the United States from Maine to Florida. Microbial community composition was examined using T-RFLP, and bacterial and fungal abundance was determined microscopically. Within the sediment, community composition was strongly correlated with latitude, indicating that biogeographical factors are important determinants of sediment community composition, whereas abundance was positively and strongly correlated with sediment organic matter content. A strong biogeographical effect was observed for both bacterial and fungal abundance on standing dead plants, but there was no clear relationship between community composition and latitude. Microbial community composition was more similar among plants of the same type (i.e., related plant species) suggesting that plant type (i.e., substrate quality) is primarily responsible for the determining community composition on standing dead plants.