Fig. 2

Comparison of log₂ ratios derived from relative abundances and after applying SCML to A. acidiphilus and R. radiobacter. Observed log₂ ratios versus expected log₂ ratios of the spike-ins A. acidiphilus and R. radiobacter as derived from (a) relative abundances and (b) SCML by S. ruber for all pairwise sample comparisons. Both approaches were performed on the raw, not adjusted read counts of A. acidiphilus and R. radiobacter. The expected log₂ ratios are calculated by the theoretical number of 16S rDNA copies predetermined in the design of the validation experiment (cf. Additional file 2: Table S2). The purple diagonal represents the identity, which represents the expected log₂ ratios by design. The box plots in (c) show the error between the expected and observed log₂ ratios for both approaches. The smaller this error, the better calibrated the ratios are