The Canonical Long-Chain Fatty Acid Sensing Machinery Processes Arachidonic Acid To Inhibit Virulence in Enterohemorrhagic Escherichia coli

Abstract

The mammalian gastrointestinal tract is a complex biochemical organ that generates a diverse milieu of host- and microbe-derived metabolites. In this environment, bacterial pathogens sense and respond to specific stimuli, which are integrated into the regulation of their virulence programs. Previously, we identified the transcription factor FadR, a long-chain fatty acid (LCFA) acyl coenzyme A (acyl-CoA) sensor, as a novel virulence regulator in the human foodborne pathogen enterohemorrhagic Escherichia coli (EHEC). Here, we demonstrate that exogenous LCFAs directly inhibit the locus of enterocyte effacement (LEE) pathogenicity island in EHEC through sensing by FadR. Moreover, in addition to LCFAs that are 18 carbons in length or shorter, we introduce host-derived arachidonic acid (C20:4) as an additional LCFA that is recognized by the FadR system in EHEC. We show that arachidonic acid is processed by the acyl-CoA synthetase FadD, which permits binding to FadR and decreases FadR affinity for its target DNA sequences. This interaction enables the transcriptional regulation of FadR-responsive operons by arachidonic acid in EHEC, including the LEE. Finally, we show that arachidonic acid inhibits hallmarks of EHEC disease in a FadR-dependent manner, including EHEC attachment to epithelial cells and the formation of attaching and effacing lesions. Together, our findings delineate a molecular mechanism demonstrating how LCFAs can directly inhibit the virulence of an enteric bacterial pathogen. More broadly, our findings expand the repertoire of ligands sensed by the canonical LFCA sensing machinery in EHEC to include arachidonic acid, an important bioactive lipid that is ubiquitous within host environments. IMPORTANCE Polyunsaturated fatty acids (PUFAs) play important roles in host immunity. Manipulation of lipid content in host tissues through diet or pharmacological interventions is associated with altered severity of various inflammatory diseases. Our work introduces a defined host-pathogen interaction by which arachidonic acid, a host-derived and dietary PUFA, can impact the outcome of enteric infection with the human pathogen enterohemorrhagic Escherichia coli (EHEC). We show that long-chain fatty acids including arachidonic acid act as signaling molecules that directly suppress a key pathogenicity island in EHEC following recognition by the fatty acyl-CoA-responsive transcription factor FadR. Thus, in addition to its established effects on host immunity and its bactericidal activities against other pathogens, we demonstrate that arachidonic acid also acts as a signaling molecule that inhibits virulence in an enteric pathogen.

FabR senses long‐chain unsaturated fatty acids to control virulence in pathogen Edwardsiella piscicida

“…UFAs significantly modulate bacterial virulence as documented in other bacterial pathogens (reviewed in Campbell & Cronan, 2001; Ellermann et al., 2021; Kovacikova et al., 2017) and observed in this study (Figure 7). Our data show that in addition to the FabR‐dependent control of esrB expression and in turn T3/T6SS production, UFAs may also modulate the expression of T3/T6SS genes in a FabR‐independent manner.…”

“…The finding of the moonlight function of FabR is of interest in connecting UFAs with pathogen virulence. UFAs, such as oleic acid (C18:1) and linoleic acid (C18:2), have been reported to inhibit virulence via distinct FadR‐dependent mechanisms in V. cholerae and enterohemorrhagic E. coli (EHEC) (Ellermann et al., 2021; Kovacikova et al., 2017; Pifer et al., 2018). In V. cholerae , FadR was described to upregulate the expression of the FA biosynthesis gene fabA , resulting in the increased ToxT levels in the absence of exogenous UFAs.…”

“…Likewise, in Salmonella enterica , free UFAs such as oleic acid (C18:1) and SFAs such as palmitic acid (C16:0) interact with HilD, leading to the impaired DNA‐binding ability of HilD and subsequent activation of SPI‐1 pathogenicity island genes (Chowdhury et al., 2021; Golubeva et al., 2016). Moreover, in enterohemorrhagic E. coli , FadR has been reported as a sensor of FAs to regulate the locus of enterocyte effacement (LEE) pathogenicity in the presence of the host‐derived long‐chain FA arachidonic acid (Ellermann et al., 2021; Pifer et al., 2018). However, whether FabR participates in the pathogenesis of pathogens remains unclear.…”

Long Chain Fatty Acids and Virulence Repression in Intestinal Bacterial Pathogens

“…More recent studies have established a link between FadR and virulence in two attaching/effacing (A/E) pathogens, enterohemorrhagic E. coli (EHEC) and C. rodentium (Pifer et al, 2018;Ellermann et al, 2021). A/E pathogens utilize type 3 secretion systems (T3SS), needle-and-syringe like structures, to translocate their effector proteins directly into host cells to establish replicative niches at the colonic epithelium (Kaper et al, 2004).…”

Transient Antibiotic Tolerance Triggered by Nutrient Shifts From Gluconeogenic Carbon Sources to Fatty Acid

“…In this work, we studied E. coli nutrient transition to FA because both FA transport and catabolic pathways are regulated by a positive feedback loop. Recent work in pathogenic bacteria has highlighted that utilization of exogenous FAs from the host environment plays a central role in regulating virulence factors in a broad-range of Gram-negative pathogens, including E. coli ( Pifer et al, 2018 ; Pan et al, 2020 ; Ellermann et al, 2021 ). Thus, nutrient transitions to FA catabolism are associated with increased pathogenicity, but these transitions remain an understudied mechanism with respect to its effect on antibiotic tolerance.…”