Distinct Metabolic Features of Pathogenic Escherichia coli and Shigella spp. Determined by Label-Free Quantitative Proteomics

Escherichia coli and Shigella spp. causing illnesses in humans represent a genotypically and phenotypically diverse group of pathogens. Although E. coli diversity has been studied by comparative genomics, the intra-species variation at the proteome level is currently unknown. The proteomes of 16 pathogenic E. coli, 2 non-pathogenic E. coli, and 5 Shigella strains originating from 18 phylogenetic lineages are investigated. By applying label-free quantitative proteomics on trypsin-digested cell extracts from bacteria grown on blood agar, 4018 proteins are detected, 3285 of which arequantified, and 261 represented virulence factors. Of 753 proteins quantified in all strains, the levels of 153 vary substantially between strains and are functionally associated mostly with stress response and peripheral metabolism. The levels of proteins associated with the central metabolism vary considerably less than the levels of proteins from other metabolic pathways. Hierarchical clustering analysis based on the protein levels results in strains grouping that differ from that obtained by gene-based phylogenetic analysis. Finally, strains of some E. coli pathotypes have more similar protein profiles even when the strains are not genetically closely related. The results suggest that the degree of genetic relatedness may not necessarily be a good predictor of E. coli phenotypic characteristics.