Figure 4.

Nutrient uptake by P. minimum measured at the single-cell level by NanoSIMS. (A) ¹⁵N-enrichment in the experiment E. (B) ¹³C-enrichment in the experiment E. (C) ¹⁵N-enrichment in the experiment F. (D) ¹³C-enrichment in the experiment F. Enrichments in ¹⁵N and ¹³C are expressed as ¹²C¹⁵N/¹²C¹⁴N and ¹³C/¹²C, respectively. “Control”—unlabeled cells; “only Nitrate”—¹⁵N-nitrate and ¹³C-bicarbonate uptake in the absence of urea; “Urea”—¹⁵N-urea and ¹³C-bicarbonate uptake in the presence of nitrate; “Nitrate”—¹⁵N-nitrate and ¹³C-bicarbonate uptake in the presence of urea. In each parallel, 15–26 cells were analyzed. The horizontal lines of Box-and-Whisker plots show the median, the hinges of the box show the 25th and 75th percentiles, and the whiskers show the entire range of ¹²C¹⁵N/¹²C¹⁴N and ¹³C/¹²C ratios. Individual values are provided in Supplementary Tables S1, S2. Enrichments of all labeled parallels are significantly higher than the enrichment of “Control” cells (Kruskal-Wallis test with the post-comparison Dunn's test, p > 0.05). The asterisks indicate significant differences between ¹⁵N-enrichment of the parallels “only Nitrate” and “Nitrate” (one-tailed Mann-Whitney test, p < 0.001 for both experiments) and the parallels “Nitrate” and “Urea” (Kruskal-Wallis test with the post-comparison Dunn's test, p > 0.05; one-tailed Mann-Whitney test, p < 0.001 for both experiments).