Biological air filters have been developed to reduce odor and ammonia emissions resulting from the rapidly expanding pig farm industry in many European countries. In contrast to aqueous biofilm environments, the biofilms of these filters are air-fed, allowing for extreme metabolite accumulation. The system, which is dominated by organoheterotrophic and ammonia oxidizing bacteria (AOB), thus comprises an extreme microbial habitat with high loads of organic acids and ammonia (up to 400 mM) and accumulation of toxic metabolites such as nitrite (reaching 300 mM). Furthermore, the filters show strong concentration gradients as both substrate load and metabolite accumulation decreases across the filter. To investigate bacterial activity, distribution, and community structure, an in situ approach was applied combining microsensor analysis in intact biofilm of a full-scale biofilter with fluorescence in situ hybridization (FISH) and cloning/sequencing of 16S rRNA genes. In the biofilm, the presence of AOB was restricted to a discrete zone between a dense surface layer of heterotrophs and an anoxic layer below. On filter level, both abundance and potential activity of the AOB increased from the filter front towards the outlet. In contrast, heterotrophic activity, as shown by microscale oxygen profiles, decreased significantly across the filter, indicating substrate limitation. Remarkably, AOB showed to be both present and active under the extreme conditions prevailing in the biofilm. However, AOB activity and abundance depended strongly on (micro)sites of heterotrophic substrate limitation and decreased NH3/HNO2 accumulation. Both factors were clearly acting as strong mechanisms controlling the distribution of ammonia oxidation in the filter.
Hidden Powers - Microbial Communities in Action. Proceedings of the 11th International Symposium on Microbial Ecology (isme-11). Vienna, Austria, 2006
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11th International Symposium on Microbial Ecology, 2006