Different cellular origins and functions of extracellular proteins from Escherichia coli O157:H7 and O104:H4 as determined by comparative proteomic analysis

Authors: ISLAM, NAZRUL - University Of Maryland; Nagy, Attila; Garrett, Wesley; Shelton, Daniel; Cooper, Bret; Nou, Xiangwu

Submitted to: Applied and Environmental Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/4/2016
Publication Date: 5/13/2016
Publication URL: http://handle.nal.usda.gov/10113/5852181
Citation: Islam, N., Nagy, A., Garrett, W.M., Shelton, D.R., Cooper, B., Nou, X. 2016. Different cellular origins and functions of extracellular proteins from Escherichia coli O157:H7 and O104:H4 as determined by comparative proteomic analysis. Applied and Environmental Microbiology. doi: 10.1128/aem.00977-16.

Interpretive Summary: E. coli O157:H7 and O104:H4 are two of the most virulent human foodborne pathogens. In this work we compared the sets of secreted proteins from each of these two strains growing in nutrient poor minimal medium. The secreted proteins were determined using proteomic approaches. Cell surface proteins typical for each strain (i.e. flagella) were detected. The major differences between the sets of secreted proteins of these two strains was the the large quantity of cytoplasmic proteins and Shiga toxin secreted by O104:H4. These data suggest that these two strains use very different pathways to respond to growth in stressful environments. The information will be useful for other scientists in better understanding the growth, survival, and persistence of these two pathogens.

Technical Abstract: Escherichia coli is a diverse species of bacteria, including several pathotypes that cause a variety of diseases in humans. Enterohemorrhagic E. coli (EHEC) and recently emerged shigatoxingenic enteroaggregative E. coli (EAEC) produce Shigatoxins and are major foodborne pathogens that can cause hemolytic uremic syndrome (HUS). We hypothesize that secreted and surface-associated proteins in E. coli may contribute to bacterial persistence in food products and environmental matrices and to human pathogenicity. In this study, secreted proteins were isolated from the supernatants of E. coli O157:H7 and O104:H4 cultures and analyzed by liquid chromatography-tandem mass spectrometry. We identified 500 and 859 proteins from the growth medium of E. coli O157:H7 and O104:H4, respectively, including 371 common to both strains. Among proteins that were considered unique to E. coli O157:H7 or present at increased abundances in O157:H7 growth medium, most (57 of 65) had secretion signal sequences in their encoding genes. Noticeably, they include LEE encoded virulence factors, proteins required for petidyl-lipoprotein accumulation, and proteins involved in iron scavenging. In contrast, a much smaller proportion (67 of 278) of proteins found only in the growth medium of E. coli O104:H4, or presented at increased abundance, had signals targeting them for secretion. These proteins included serine protease autotransporters, shigatoxin 2 subunit B, and O104:H4 signature proteins including AAF/1 major fimbrial subunit and beta-lactamase. The majority of the proteins from the growth medium of E. coli O104:H4 was annotated as having functions in the cytoplasm. We provide evidence that the extensive presence of cytoplasmic proteins in E. coli O104:H4 growth medium was not due to cell lysis, indicating alternative mechanisms for this potent pathogen releasing cytoplasmic contents into the growth milieu, which could promote biofilm formation and enhance its survival in adverse environments. The significant differences between the compositions of the secreted proteins among these two major types of foodborne pathogenic E. coli seem to suggest different pathways to respond to environmental stresses.