Presentation: 2025 ND EPSCoR Annual conference 

October 21, 2025, NDSU Memorial Union, Fargo, North Dakota

Investigating Mechanisms of Iron Import Cell-Surface Signaling Activation in Escherichia coli and Pseudomonas capeferrum

In Gram-negative bacterial iron import pathways, TonB-dependent transporters (TBDTs) move iron across the outer membrane. Expression of a subset of TBDTs can be upregulated through cell-surface signaling (CSS). This type of CSS is a highly conserved process by which bacteria rapidly respond to extracellular stimuli via transcriptional regulation. TBDTs that contain an additional N-terminal signaling domain (NTSD) are involved in CSS. The three key protein components in import CSS pathways include: 1) the NTSD containing TBDT, 2) an inner membrane sigma regulator, and 3) an extra-cytoplasmic function sigma factor. Under conditions of low iron, Gram-negative bacteria secrete iron chelating molecules, called siderophores to scavenge iron from the environment. When the bacteria encounters iron laden siderophore, the expression of the TBDT is upregulated by CSS. Signaling is mediated by the interaction of the NTSD with the C-terminal cell-surface signaling domain (CCSSD) of an inner membrane (IM) sigma regulator. In this work, we look to elucidate unknown aspects concerning the interaction between the TBDT FecA and the CCSSD of the sigma regulator FecR from Escherichia coli as well as the TBDT PupB and the CCSSD of the sigma regulator PupR from Pseudomonas capeferrum. The understanding of the interaction between the TBDT and sigma regulator will provide key structural information about how CSS is initiated.