Fig. 1.

Log₂ transformed read counts of the three spike-in bacteria as a function of total microbial load. S. ruber was added at a constant number of 16S rDNA copies, while A. acidiphilus and R. radiobacter were spiked in variably (cf. Additional file 2: Table S2). a Resulting read counts of A. acidiphilus and R. radiobacter versus spiked-in 16S rDNA copies at different background stool microbiota dilutions. Each dot represents a caecal specimen, while the colour specifies its dilution. b Boxplots showing the read counts of all three spike-in bacteria as a function of total microbial load. The log₂ read counts of S. ruber are coloured blue, while A. acidiphilus and R. radiobacter are coloured red and green, respectively. Read counts of A. acidiphilus and R. radiobacter were adjusted by a factor corresponding to their difference of the predefined spike-in concentration to S. ruber. The x-axis is discrete and represents increasing stool dilution (bottom), as well as decreasing microbial load from left to right (grey arrowhead on the top)