TABLE 1.

Quantitative Proteomic Approaches utilized to studying GC.

Proteomic Approach	Principles	Use in GC	References
Isotope coded affinity tag (ICAT)	- Post-harvest labeling - Heavy or light isotopic reactive groups label cysteine residues in a protein sample. - Two samples are pooled and analyzed by MS. - Relative quantification of proteins by comparing heavy: light ratio.	Response to oxidative stress	Wu et al. (2010)
Stable isotope labeling by amino acids in cell culture (SILAC)	- Metabolic labeling - Growth medium is supplemented with either light (unlabeled) or heavy (labeled) amino acid. - Two samples are pooled and analyzed by MS. - Relative quantification of proteins by comparing heavy: light ratio	Shift from planktonic to biofilm growth	Phillips et al. (2012)
Isobaric Tagging for Relative and Absolute Quantification (iTRAQ)	- Post-harvest labeling - Proteolytically digested proteins are tagged on N-termini and lysine side chains with isobaric mass labels. - Two to eight samples are pooled and analyzed by MS. - Relative or absolute quantification of proteins by measuring intensity of reporter ion peak.	Cell envelopes and membrane vesicles Comparison of cell envelope profiles upon environmental cues encountered in the host	Zielke et al. (2014); Zielke et al. (2015)