Bollmann, A. and Schmidt, I. and Saunders, A.M. and Nicolaisen, M.H. (2005) Influence of Starvation on Potential Ammonia-Oxidizing Activity and amoA mRNA Levels of Nitrosospira briensis. Applied and Environmental Microbiology, 71, 1276-1282. ISSN 0099-2240.
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Official URL: http://dx.doi.org/10.1128/AEM.71.3.1276-1282.2005
The effect of short-term ammonia starvation on Nitrosospira briensis was investigated. The ammonia-oxidizing activity was determined in a concentrated cell suspension with a NOx biosensor. The apparent half-saturation constant [Km(app)] value of the NH3 oxidation of N. briensis was 3 µM NH3 for cultures grown both in continuous and batch cultures as determined by a NOx biosensor. Cells grown on the wall of the vessel had a lower Km(app) value of 1.8 µM NH3. Nonstarving cultures of N. briensis showed potential ammonia-oxidizing activities of between 200 to 250 µM N h–1, and this activity decreased only slowly during starvation up to 10 days. Within 10 min after the addition of fresh NH4+, 100% activity was regained. Parallel with activity measurements, amoA mRNA and 16S rRNA were investigated. No changes were observed in the 16S rRNA, but a relative decrease of amoA mRNA was observed during the starvation period. During resuscitation, an increase in amoA mRNA expression was detected simultaneously. The patterns of the soluble protein fraction of a 2-week-starved culture of N. briensis showed only small differences in comparison to a nonstarved control. From these results we conclude that N. briensis cells remain in a state allowing fast recovery of ammonia-oxidizing activity after addition of NH4+ to a starved culture. Maintaining cells in this kind of active state could be the survival strategy of ammonia-oxidizing bacteria in nature under fluctuating NH4+ availability.
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