Fig. 6.

Venn diagram of the number of unique spectra (cutoff: protein probability 90%, minimum peptides 1, minimum peptide probability 95%) obtained in the spiking experiment. The upper part shows the experimental bias by comparing the numbers of unique spectra for the pure culture and the subsequent recovery from the spiked soil sample for both protocols (NaOH, extraction based on sodium hydroxide with further phenol purification; SP extraction with SDS and phenol). The lower venn diagrams depict the methodological bias by showing the number of unique spectra that could be found with either one or both protocols.