(703b) Inter-Kingdom Signaling and Chemotaxis of E. Coli towards the Human Hormone Norepinephrine

Sasi Kiran Pasupuleti^a, Mathew Sears^b, Michael D. Manson^b, Arul Jayaraman^a

Department of Chemical Engineering^aand Department of Biology^b, Texas A&M University, College Station, Texas 77840.

Abstract

The co-existence of ~10¹⁴non-pathogenic commensal bacteria and human mucosa cells (intestinal epithelial cells, dendritic cells, macrophages) in the human gastrointestinal (GI) tract creates an environment rich in molecules produced by both the bacteria (e.g., autoinducer-2, indole) and the host (e.g., norepinephrine, dopamine). The close-proximity of different signals and cells is thought to lead to inter-kingdom signaling where bacteria and human cells recognize and respond to signals produced by the other kingdom. Prior work from our lab [1] has shown that pathogenic bacteria are attracted towards higher concentrations of host-produced hormones (i.e., chemotaxis) and this migration correlates with an increase in pathogen virulence and invasion of host cells [2]. However, the mechanisms through which NE is sensed by pathogenic bacteria are poorly understood.

In this study, we investigated the mechanisms underlying the inter-kingdom recognition and chemotaxis towards norepinephrine using E. coli as the model bacterium. Using isogenic mutant strains and a microfluidic chemotaxis model (µFlow) developed in our laboratory [2], we identified that chemotaxis towards norepinephrine requires the serine chemoreceptor (Tsr), and that Tsr is both necessary and sufficient for norepinephrine chemotaxis. The shape of the concentration gradient was important, as chemotaxis was observed only in the presence of a sharp concentration gradient, and not in shallow concentration gradients. We further identified that the serine majority binding site (T156), but not the minority binding site (R69), is required for norepinephrine chemotaxis. We also observed that a robust chemotactic response was observed only when bacteria were pre-exposed to norepinephrine, as untreated cells did not move towards higher concentrations in a norepinephrine concentration gradient. Therefore, we hypothesized that priming bacteria with norepinephrine results in de novo synthesis of protein(s) required for chemotaxis towards norepinephrine. Pre-exposure to norepinephrine in the presence of a protein synthesis inhibitor abolished the chemotaxis in a norepinephrine gradient and confirmed the need for de novo protein synthesis. Preliminary qRT-PCR studies identified that the enzyme monoamine oxidase A (maoA), which converts norepinephrine to 3,4-dihydroxyphenylglycolaldehyde in the GI tract, is up-regulated in E. coli upon norepinephrine priming. Our results suggest a novel chemotaxis mechanism in which the invading pathogen metabolizes an abundant molecule such as norepinephrine that is present in the microenvironment to generate a metabolite that is then used as a potent chemoattractant. 

References

[1] Bansal, T., et al., Differential effects of epinephrine, norepinephrine, and indole on Escherichia coli O157:H7 chemotaxis, colonization, and gene expression. Infection and immunity 75:4597–4607. [2] Englert, DL., et al., Investigation of bacterial chemotaxis in flow-based microfluidic devices. Nature Protocols 5, -864 - 872 (2010).  [2] Englert, DL., et al., Investigation of bacterial chemotaxis in flow-based microfluidic devices. Nature Protocols 5, -864 - 872 (2010).