Advanced tool for characterization of microbial cultures by combining cytomics and proteomics

Flow cytometry approaches are applicable to recover sub-populations of microbial cultures in a purified form. To examine the characteristics of each sorted cell population, Omics technologies can be used for comprehensively monitoring cellular physiology, adaptation reactions, and regulated processes. In this study, we combined flow cytometry and gel-free proteomic analysis to investigate an artificial mixed bacterial culture consisting of Escherichia coli K-12 and Pseudomonas putida KT2440. Therefore, a filter-based device technique and an on-membrane digestion protocol were combined in conjunction with liquid chromatography and mass spectrometry. This combination enabled us to identify 903 proteins from sorted E. coli K-12 and 867 proteins from sorted P. putida KT2440 bacteria from only 5 x 10(6) cells of each. Comparative proteomic analysis of sorted and non-sorted samples was done to prove that sorting did not significantly influence the bacterial proteome profile. We further investigated the physicochemical properties, namely M (r), pI, hydropathicity, and transmembrane helices of the proteins covered. The on-membrane digestion protocol applied did not require conventional detergents or urea, but exhibited similar recovery of all protein classes as established protocols with non-sorted bacterial samples.