Protein stable isotope fingerprinting (P-SIF): Synechocystis sp. PCC6803 + Allochromatium vinosum DSM180 biomass mixture

Protein stable isotope fingerprinting (P-SIF) is a method to measure the carbon isotope ratios of whole proteins separated from complex mixtures, including cultures and environmental samples. The goal of P-SIF is to expose the links between identity and function in microbial ecosystems by (i) determining the values of δ13C for different taxonomic divisions, and (ii) using those values as clues to the metabolic pathways employed by the respective organisms. This project develops a two-dimensional HPLC protocol followed by tryptic digestion and isotope ratio mass spectrometry on fraction aliquots. Data from a mixture of Synechocystis sp. PCC6803 and A. vinosum DSM180 biomass show that P-SIF can predict the δ13C values of the original taxa. The measured values of δ13C along with the QTOF-MS/MS peptide signal intensity and protein assignments are used in an overdetermined set of linear equations to back-calculate the values of δAllo and δSyn for the individual species. These data suggest the approach will be useful to determine natural δ13C signatures in microbial ecosystems.