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Applied and Environmental Microbiology, June 2009, p. 3705-3713, Vol. 75, No. 11
0099-2240/09/$08.00+0 doi:10.1128/AEM.02612-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.

Lars D. M. Ottosen, and
Lars Peter Nielsen
Department of Biological Sciences, Microbiology, Aarhus University, Bd. 1540, DK-8000 Aarhus C, Denmark
Received 14 November 2008/ Accepted 30 March 2009
The in situ activity and distribution of heterotrophic and nitrifying bacteria and their potential interactions were investigated in a full-scale, two-section, trickling filter designed for biological degradation of volatile organics and NH3 in ventilation air from pig farms. The filter biofilm was investigated by microsensor analysis, fluorescence in situ hybridization, quantitative PCR, and batch incubation activity measurements. In situ aerobic activity showed a significant decrease through the filter, while the distribution of ammonia-oxidizing bacteria (AOB) was highly skewed toward the filter outlet. Nitrite oxidation was not detected during most of the experimental period, and the AOB activity therefore resulted in NO2–, accumulation, with concentrations often exceeding 100 mM at the filter inlet. The restriction of AOB to the outlet section of the filter was explained by both competition with heterotrophic bacteria for O2 and inhibition by the protonated form of NO2–, HNO2. Product inhibition of AOB growth could explain why this type of filter tends to emit air with a rather constant NH3 concentration irrespective of variations in inlet concentration and airflow.
Published ahead of print on 10 April 2009.
Present address: Leibniz University Hannover, Institute for Microbiology, Schneiderberg 50, D-30167 Hannover, Germany.
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