Fig. 3: Ammonium and urea assimilation by Nitrosopelagicus, Nitrosopumilus and other microorganisms.
From: Urea use drives niche separation between dominant marine ammonia oxidizing archaea
Representative CARD-FISH images from the Black Sea (Station S3, 104 m) of a Nitrosopelagicus WCA (targeted by the specific probe Npe_WCA_226 in pink; counterstained by DAPI, white) and corresponding NanoSIMS image of 15N/(14N + 15N) enrichment after addition of 15N-urea + 14N-ammonium and b Nitrosopumilus (targeted by the specific probe Npum_229 in blue; counterstained by DAPI, white) and corresponding NanoSIMS image of 15N/(14N + 15N) enrichment after addition of 15N-ammonium. Target cells are marked by white outlines. Scale bar, 2 μm. Note the different scales for 15N/(14N + 15N) enrichment in a, b. c 15N/(14N + 15N) enrichment of Nitrosopelagicus WCA (magenta), Nitrosopumilus (blue) and other microorganisms (gray) after incubation with 15N-ammonium and urea (+14N-ammonium). Boxplots depict the 25–75% quantile range, with the center line depicting the median (50% quantile); whiskers encompass data points within 1.5× the interquartile range. Dashed lines represent the limit of detection. Cells that were below the limit of detection are filled white. Natural abundance of 15N/(14N + 15N) is 3.7 × 10−3. 15N at% enrichment of the substrate pools (ammonium or urea, respectively) was >97%. One value for Nitrosopelagicus on ammonium is not depicted (3.3 × 10−2) but was included in all calculations. Note the different y-axis scales. n = number of measurements per group and treatment with number of cells enriched significantly above the detection limit in brackets. *** indicates significant difference between treatments in two-sided Mann–Whitney–Wilcoxon tests. Nitrosopelagicus had similar enrichment values from 15N-ammonium and 15N-urea (W = 335, P value = 0.45). 15N/(14N + 15N) enrichment of Nitrosopelagicus on 15N-urea vs 15N-urea + ammonium was similar, but significantly different (W = 156, P value = 0.017). Nitrosopumilus and other microorganisms were significantly higher enriched after incubation with 15N-ammonium compared to 15N-urea (W = 305, P value = 1.2 × 10−5 and W = 3337, P value = 1.5 × 10−6, respectively). Their enrichment dropped significantly, when an additional pool of 14N-ammonium was present (W = 397, P value = 3.8 × 10−5 and W = 2990.5, P value = 3.0 × 10−4, respectively). All statistical parameters and source data are provided as a Source Data file.
