Figure 1.

Growth and activity of Ca. N. exaquare. (a) Growth curve, indicating conversion of 1 mm ammonia to nitrite and corresponding increase in thaumarchaeotal cell numbers. Cell numbers were estimated by thaumarchaeotal 16S rRNA gene copy numbers, halved to account for two 16S rRNA gene copies per genome. (b) Ca. N. exaquare nitrite production at varying incubation temperatures. (c) Depletion of 0.5 mm ammonia by Ca N. exaquare at varying initial nitrite concentrations. Starting nitrite concentrations are indicated in the panel legend. For this panel, ammonia depletion is shown due to high background levels of nitrite. (d) Ca. N. exaquare nitrite production at varying starting ammonia concentrations. Starting ammonia concentrations are indicated in the panel legend. Note that nitrite production plateaus in the 0.5 mm condition due to depletion of supplied ammonia. All incubations were prepared from a 1% inoculum from an actively growing enrichment culture and were performed in the dark, without shaking. Unless otherwise indicated, the incubation temperature was 30 °C. Error bars indicate the standard error of the mean for biological triplicates. Error bars not seen are contained within the symbols.