Ethanolamine Influences Human Commensal Escherichia coli Growth, Gene Expression, and Competition with Enterohemorrhagic E. coli O157:H7

Abstract

A core principle of bacterial pathogenesis is that pathogens preferentially utilize metabolites that commensal bacteria do not in order to sidestep nutritional competition. The metabolite ethanolamine (EA) is well recognized to play a central role in host adaptation for diverse pathogens. EA promotes growth and influences virulence during host infection. Although genes encoding EA utilization have been identified in diverse bacteria (nonpathogenic and pathogenic), a prevailing idea is that commensal bacteria do not utilize EA to enhance growth, and thus, EA is a noncompetitive metabolite for pathogens. Here, we show that EA augments growth of two human commensal strains of Escherichia coli Significantly, these commensal strains grow more rapidly than, and even outcompete, the pathogen enterohemorrhagic E. coli O157:H7 specifically when EA is provided as the sole nitrogen source. Moreover, EA-dependent signaling is similarly conserved in the human commensal E. coli strain HS and influences expression of adhesins. These findings suggest a more extensive role for EA utilization in bacterial physiology and host-microbiota-pathogen interactions than previously appreciated.IMPORTANCE The microbiota protects the host from invading pathogens by limiting access to nutrients. In turn, bacterial pathogens selectively exploit metabolites not readily used by the microbiota to establish infection. Ethanolamine has been linked to pathogenesis of diverse pathogens by serving as a noncompetitive metabolite that enhances pathogen growth as well as a signal that modulates virulence. Although ethanolamine is abundant in the gastrointestinal tract, the prevailing idea is that commensal bacteria do not utilize EA, and thus, EA utilization has been particularly associated with pathogenesis. Here, we provide evidence that two human commensal Escherichia coli isolates readily utilize ethanolamine to enhance growth, modulate gene expression, and outgrow the pathogen enterohemorrhagic E. coli These data indicate a more complex role for ethanolamine in host-microbiota-pathogen interactions.

Keywords: ethanolamine; metabolism; microbiota; signaling.

FIG 1

EA-dependent growth and signaling in E. coli HS. (A) Growth curve of HS grown in minimal medium with indicated EA concentrations. n = 3. OD₆₀₀, optical density at 600 nm. (B) Growth curve of wild type (WT) with empty vector, ΔeutR mutant with empty vector, and eutR complemented strain grown in minimal medium containing EA. n = 3. (C) Growth curve of HS grown in minimal medium with indicated carbon and nitrogen sources or without vitamin B₁₂, as specifically indicated. n = 3. (D) Bacterial cell density at indicated time points after growth in minimal medium with NH₄ or NH₄ and EA. n = 3. (E) Reverse transcription-quantitative PCR (qRT-PCR) of eut gene expression in HS grown in in minimal medium with NH₄ or NH₄ and EA. n = 3. (F) qRT-PCR of fimbrial genes in HS grown in minimal medium with NH₄ or NH₄ and EA. n = 6. For all, unless indicated, vitamin B₁₂ was added whenever the medium was supplemented with EA. Error bars represent the mean ± standard deviation (SD). **, P ≤ 0.01; ***, P < 0.001.

FIG 2

HS outcompetes EHEC specifically during growth on EA. (A) Growth curve of E. coli HS and EHEC in minimal medium with EA and glucose. (B) Competition assay between E. coli HS and EHEC in minimal medium with EA and glucose. (C) Growth curve of E. coli HS and EHEC in minimal medium with EA and glycerol. (D) Competition assay between E. coli HS and EHEC in minimal medium with EA and glycerol. For panels A to D, vitamin B₁₂ was added to the medium. (E) Growth curve of E. coli HS and EHEC in minimal medium with NH₄ and glucose. (F) Competition assay between E. coli HS and EHEC in minimal medium with NH₄ and glucose. For all, n equals 3; error bars represent the mean ± standard deviation. *, P ≤ 0.05; **, P ≤ 0.01; ns, P > 0.05.