title: Influence of starvation on potential ammonia-oxidizing activity and amoA mRNA levels of Nitrosospira briensis.
abstract: 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 microM 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 microM NH3. Nonstarving cultures of N. briensis showed potential ammonia-oxidizing activities of between 200 to 250 microM 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.
authors.affiliation: Department of Microbial Ecology, Institute of Biological Sciences, University of Aarhus, Aarhus, Denmark. a.bollmann@neu.edu
authors.forename: Annette
authors.initials: A
authors.lastname: Bollmann
authors.forename: Ingo
authors.initials: I
authors.lastname: Schmidt
authors.forename: Aaron M
authors.initials: AM
authors.lastname: Saunders
authors.forename: Mette H
authors.initials: MH
authors.lastname: Nicolaisen
mesh_terms: D000114:Acetylene / Q000494:pharmacology; D000641:Ammonia / Q000378:metabolism*; D001483:Base Sequence; D003470:Culture Media; D004269:DNA, Bacterial / Q000235:genetics; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005798:Genes, Bacterial; D007700:Kinetics; D043369:Nitrosomonadaceae / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D010084:Oxidation-Reduction; D010088:Oxidoreductases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012329:RNA, Bacterial / Q000235:genetics* / Q000378:metabolism*; D012333:RNA, Messenger / Q000235:genetics* / Q000378:metabolism*; D012336:RNA, Ribosomal, 16S / Q000235:genetics / Q000378:metabolism
chemical_list: D003470:Culture Media; D004269:DNA, Bacterial; D004791:Enzyme Inhibitors; D012329:RNA, Bacterial; D012333:RNA, Messenger; D012336:RNA, Ribosomal, 16S; D000641:Ammonia; D010088:Oxidoreductases; C045582:ammonia monooxygenase; D000114:Acetylene