Fig. 3.

Intact cell membrane/viable bacterial and fungal population aboard the ISS as estimated by PMA-qPCR. a Scatter plot comparing the 16S rRNA gene (bacteria) and ITS region (fungi) copy numbers of PMA treated samples collected during flights 1, 2, and 3. Each column represents a single flight and each symbol in a column (labeled with a number) represents one of the eight locations sampled during that flight. The horizontal line in each column represents the average gene copy number/m² for each Flight. b Scatter plot comparing 16S rRNA gene and c ITS region (fungi) copy numbers across locations. Each column “L” followed by a number represents a location and each dot in a column represents the flight it was sampled from. The horizontal line in each column represents the average copy number/m² at that location. NB: The 16S rRNA gene copy number was not adjusted to the average number per bacterial genome. Control samples were measured and found to be at the level of 10² 16S rRNA gene copies per μL. Even when the initial template volume was increased to 10 μL, the expected 20-fold increase in the gene copy numbers was not observed. In panel a, F1-ITS was statistically significantly higher than F3-ITS (P < 0.05). No statistically significant differences were observed in panel b (P > 0.05). The statistical test was performed with the Kruskal-Wallis test followed by Dunn’s post-hoc test