Microbial resource management: from high throughput models to pilot reactors

Titel:	Microbial resource management: from high throughput models to pilot reactors
Kategorie:	Seminar Umweltmikrobiologie
Detail:	Gastvorlesung
Datum:	18. Dez. 2012, 16:00 Uhr -
Ort:	Eawag Dübendorf
	BU-G3
Referenten:	Nico Boon
Organisation:	Department of Microbial and Biochemical Technology, Ghent University
Kosten:	kostenlos/free
Download:	als Kalender-Eintrag

The biodiversity-stability relationship between microbial communities and the effect of biodiversity on functioning and invasion have become a major focus in research. While previous studies have mainly focused on how a higher level of species richness can confer a greater stability to specific ecosystem properties, the relationship between functionality, invasion and evenness has not been deeply investigated.

In a first study, the impact of initial community evenness on the functionality of the resident community was assessed by the use of assembled denitrifying bacterial communities; this approach is well suited for validating ecological theories (2). To exclude confounding factors, the tests were conducted with (i) a complex medium to avoid nutrient limitation and (ii) an assembled community composed of bacteria occupying the same functional niche (the capability for nitrite respiration) and isolated from the same sample of homogenised activated sludge. A total of 17! denitrifying strains from 4 phyla were mixed in different proportions to create a few thousand microcosms with different levels of initial evenness but with the same richness. In a first set of experiments, we demonstrated that provided a good level of functional redundancy within microbial populations, the relative degree of evenness plays an important role in conserving a given functionality at short terms under perturbed conditions.

In a follow up study, the degree of invasion of an introduced species (a non-denitrifier) was evaluated and the final effect of this invader on the functionality of the denitrifying community (4). We showed that evenness influences the level of invasion into a community and that the introduced species can promote functionality under specific environmental stressors. The evenness-invasibility relationship was negative in the absence of salinity stress and neutral in the presence of salinity stress. Under such a stress condition, the introduced species is able to maintain the functionality of unevencommunities. These results indicate that the invasibility of the ecosystem depends strongly on both the environmental conditions and the evenness of the resident community. Furthermore, an introduced species - generally considered negative - can also be an added value to the community and its functionality.

Besides evenness, richness and the dynamics of change are also postulated to be of importance for functional stability (3). This biodiversity-stability relationship was examined in a granular activated carbon (GAC) filtration (5). GAC filtration is essentially a microbial process that removes all biodegradable organic carbon from the ozonated water and ensures biological stability of the treated water. In this study, the start-up and maturation of an undisturbed pilot-scale GAC filter was monitored at 4 depths (10-45-80-115 cm) over a period of 6 months. New ecological tools, based on DGGE, were linked to filter performance and microbial activity (1) and showed that the stratification in a GAC reactor was of importance. At 10cm, receiving the freshly ozonated water, microbial activity was inhibited by residual ozone. This was reflected in the microbial community where no changes were observed and the richness remained low. However, the GAC samples at 80-115cm showed a 2-3 times higher richness then the 10-45cm samples. The highest biomass densities were observed at 45-80cm, which corresponded with maximum removal of dissolved and assimilable organic carbon. Furthermore, the start-up period was clearly visible from Pareto analysis: after two months, the community shifted to a more even organisation, which was accompanied by an apparent steady state condition. In conclusion, this study clearly shows that microbial community analysis can be linked to a good reactor performance. In the GAC filter sections with high activity, a high richness and evenness is needed for good performance. Moreover, these good performing microbial communities are 4 times more dynamic than the less performing communities.