Distribution of protein abundances. The average number of MS/MS spectra was calculated for each protein from two normalized shotgun experiments done on cells harvested in the exponential phase (Table S8 in Additional data file 2). Normalization was done on total MS/MS spectra. The proteins were ranked as a function of their average number of MS/MS spectra from the most to the least detected. The graph reports the percentage of cumulative MS/MS spectra per number of proteins considered.