Comparison of Nitrosospira strains isolated from terrestrial environments

Abstract

Most of our knowledge about the physiology of ammonia-oxidizing bacteria is based on experiments with Nitrosomonas europaea, which appears to be less ubiquitous than Nitrosospira. We have isolated Nitrosospiras from widely different environments and compared their specific growth rate, substrate affinity, urease activity, temperature response, pH tolerance and cell morphology. Two of the strains had a variable morphology: the spirals were less tightly coiled than the classical Nitrosospira type and a fraction of the culture had a vibrioid appearance. These vibrioid strains were also peculiar in having a much higher apparent activation energy for ammonia monooxygenase (AMO) (129 and 151 kJ mol(-1)) than that of the more classical Nitrosospiras (78 and 79 kJ mol(-1)). The differences in morphology and activation energy were congruent with the phylogeny of the genes for 16S rRNA (Utåker et al., System. Appl. Microbiol. 18) and AMO. The response to pH in the medium was investigated for four strains. The oxidation rate at the onset of the pH exposure experiment was found to obey classical steady state enzyme kinetics, assuming that NH(3) (not NH(4)(+)) is the rate-limiting substrate. The calculated half saturation constants (K(s)) for AMO were 6-11 µM NH(3). Growth had a narrower pH range than oxidation activity and appeared to be restricted by pH-dependent factors other than NH(3). All the isolated strains were urease positive, with a specific urease activity ranging from 60 to 158% of their specific AMO activity. The urease activity was unaffected by acetylene inhibition of the energy metabolism. The substrate affinity for one strain was found to be around 670 µM.

Genera-Specific Immunofluorescence Labeling of Ammonia Oxidizers with Polyclonal Antibodies Recognizing Both Subunits of the Ammonia Monooxygenase

“…Electron microscopic investigations of the same cultures revealed characteristic cells with a morphology and ultrastructure of small Nitrosolobus sp. cells (Schnier, personal communication), which is in agreement with recent studies in which Nitrosolobus [32,49] and Nitrosospira [6,19,21,25] were the most abundant ammonia oxidizers in loamy and arable soils with neutral pH.…”

The Biogeography of Ammonia-Oxidizing Bacterial Communities in Soil

“…The results from this study do not provide the answer, but we can hypothesize that distinct phylogenetic groups may have distinct temperature optima. This has been demonstrated with Nitrosospira strains grown in pure culture [47] and with AOB communities from different soils [48]. If these observations are generalizable and there is minimal functional redundancy between taxa (i.e., phylogenetically distinct communities have distinct temperature sensitivities), it may explain why the temperature responses in nitrification activity can vary so widely across different soils [49,50] or sediment samples [51].…”

Comparison of nitrifier activity versus growth in the Scheldt estuary—a turbid, tidal estuary in northern Europe

“…(1) bacteria may use an additional energy source or stored energy reserves, (2) community composition of ammonium-oxidizing bacteria in the estuary may vary over time and/or space, and these different communities may have variable optimal N:C ratios; metabolic activity and growth rates can differ among cultures (Jiang & Bakken 1999b) and thus also among different communities, (3) our N:C ratios may have been biased towards low values because of our neglect of ammonium regeneration that caused dilution of 15 N, and (4) low N:C ratios coincided with low oxygen concentrations i.e. <100 µM.…”