Driving the expression of the Salmonella enterica sv Typhimurium flagellum using flhDC from Escherichia coli results in key regulatory and cellular differences

Abstract

The flagellar systems of Escherichia coli and Salmonella enterica exhibit a significant level of genetic and functional synteny. Both systems are controlled by the flagellar specific master regulator FlhD4C2. Since the early days of genetic analyses of flagellar systems it has been known that E. coli flhDC can complement a ∆flhDC mutant in S. enterica. The genomic revolution has identified how genetic changes to transcription factors and/or DNA binding sites can impact the phenotypic outcome across related species. We were therefore interested in asking: using modern tools to interrogate flagellar gene expression and assembly, what would the impact be of replacing the flhDC coding sequences in S. enterica for the E. coli genes at the flhDC S. entercia chromosomal locus? We show that even though all strains created are motile, flagellar gene expression is measurably lower when flhDCEC are present. These changes can be attributed to the impact of FlhD4C2 DNA recognition and the protein-protein interactions required to generate a stable FlhD4C2 complex. Furthermore, our data suggests that in E. coli the internal flagellar FliT regulatory feedback loop has a marked difference with respect to output of the flagellar systems. We argue due diligence is required in making assumptions based on heterologous expression of regulators and that even systems showing significant synteny may not behave in exactly the same manner.

Physical Extraction and Fast Protein Liquid Chromatography for Purifying Flagella Filament From Uropathogenic Escherichia coli for Immune Assay

“…We note that our use of a fliC mutant in these assays reflects a crucial control to conclude that the proinflammatory responses induced by FliC are not an artifact secondary to LPS contamination, which is an important consideration in studies of this type (Eaves-Pyles et al, 2001). We also point out that our expression system is based on Serratia flhDC , which may be a limitation to our study given a recent observation that heterologous expression of regulators that control flagella expression systems may not behave in exactly the same manner, even in systems that show significant synteny (Albanna et al, 2018). In the broader content of bacterial pathogenesis, Salmonella flagella, which occur with two antigenically distinct forms of flagellin, FliC and FljB (Eom et al, 2013), induce proinflammatory responses that encompass TNF-α, IL-1β, and IL-6 in human cells and mice (Ciacci-Woolwine et al, 1997; Mcdermott et al, 2000; Moors et al, 2001) and that appear to be independent of different flagellin variants (Horstmann et al, 2017).…”

Agaric acid reduces Salmonella biofilm formation by inhibiting flagellar motility

“…The flagellar systems of E. coli and Salmonella show a high degree of similarity on the genetic and functional level [ 29 ]. Moreover , E. coli also requires normal flagellar function in order to successfully adhere to an abiotic surface [ 30 ].…”

Filtering input fluctuations in intensity and in time underlies stochastic transcriptional pulses without feedback

“…Our current analysis opens up a few directions for future investigation. Experimentally, effects of the filter-and-integration mechanism may be tested by perturbing the two key factors, for example, by tuning the strength of the interaction between FlhDC and class 2 promoters (32,38) or by reducing the effective concentration of YdiV by adding Salmonella FlhC known to have weaker affinity for E. coli promoters but the same affinity for YdiV as E. coli FlhC (39). It would be highly informative to measure single-cell gene expression dynamics of Salmonella in the mother machine as done for E. coli (19), to understand its gene regulation strategy quantitatively.…”