Fig. 2.

Bacterial cell counting using SRM. Construction of a stoichiometry density models relies on measurement of the number of cells injected into the MS to determine copy numbers per cell. A calibration set of samples was constructed based on serial dilutions of eight different strains and the cells counted using four established counting methods followed by SRM analysis and refinement using isotope labeled reference peptides. A, Comparison of cell counts from four standard bacterial counting methods, where the red numbers are the respective Pearson's correlation coefficient. B, Visualization of the flow cytometry, microscopy and SRM data. C, Correlation of the intensity values between flow cytometry and intensity values obtained via SRM for each of the 6 Baccus peptides. D, Performance of predicted versus measured amount of bacterial cells, based on the median intensity of the Baccus peptides measured.