Activation of Motility by Sensing Short-Chain Fatty Acids via Two Steps in a Flagellar Gene Regulatory Cascade in Enterohemorrhagic Escherichia coli

Abstract

The regulated expression of virulence genes is critical for successful infection by an intestinal pathogen. Bacteria rely on sensing environmental signals to find preferable niches and reach the infectious state. Orally ingested enterohemorrhagic Escherichia coli (EHEC) travels through the gastrointestinal tract and encounters a variety of environmental factors, some of which act as triggering signals for the induction of virulence genes. Butyrate, one of the main short-chain fatty acids (SCFAs), is such a signal, enhancing the expression of genes for intimate attachment and type III secretion. We further explored the role of SCFAs and found a positive effect of SCFAs on flagellar expression. Although EHEC did not produce flagella when grown in Dulbecco's modified Eagle's medium (DMEM), a tissue culture medium that enhances virulence gene expression, the addition of SCFAs to the medium induced the production of flagella, and the EHEC bacteria became motile. Among SCFAs, butyrate simultaneously activates both virulence and flagellar genes. Flagella did not affect initial adherence, and they were not expressed in adherent bacteria during microcolony formation. SCFAs activated flagellar genes via two regulatory steps. Butyrate activated the flhDC regulatory genes through leucine-responsive regulatory protein (Lrp), which is also a regulator of virulence genes. However, butyrate, acetate, and propionate also activated downstream genes independently of flhDC activation. Consequently, when encountering increased concentrations of SCFAs, which are abundant in acetate, in the intestine, EHEC first activates flagellar production and motility, followed by genes involved in adherence and type III secretion, which leads to efficient adherence in a preferable niche.

Fatty Acids Regulate Stress Resistance and Virulence Factor Production for Listeria monocytogenes

“…On the other hand, butyrate is produced as a fermentation product by the intestinal microbiota and is associated with diverse regulatory functions, including activating virulence in enterohemorrhagic Escherichia coli (42,52) and Shiga toxin-expressing E. coli (24) and downregulating the expression of genes in Salmonella pathogenicity island I in Salmonella enterica serovar Typhimurium (11,20,32). In L. monocytogenes, although anteiso-BCFA levels were restored in butyrate-grown bacteria by 2MB, LLO production remained compromised, supporting a potential signaling role of butyrate independent of modulating FA composition.…”

The fimbriae activator MatA switches off motility in Escherichia coli by repression of the flagellar master operon flhDC

“…Accordingly, initiation of flhDC transcription constitutes the primary regulatory point of the flagellation phenotype, and the flhDC promoter responds to multiple regulatory proteins and a number of environmental as well as physiological factors, such as temperature (Adler & Templeton, 1967;Li et al, 1993), pH (Soutourina et al, 2002) and the presence of butyrate (Tobe et al, 2011). Examples of global regulators that directly target the class 1 promoter are the nucleoid protein H-NS (Bertin et al, 1994;Soutourina et al, 1999), the catabolite repressor CRP (Silverman & Simon, 1974;Soutourina et al, 1999), the response regulator RcsB with its accessory cofactor RcsA (Francez-Charlot et al, 2003) and the quorum-sensing regulators QseBC (Clarke & Sperandio, 2005;Sperandio et al, 2002).…”

The Interplay between the Microbiota and Enterohemorrhagic Escherichia coli

“…Butyrate, but not acetate or propionate, is capable of inducing T3S from the Sakai strain of EHEC (69); 20 mM butyrate increases adhesion to Caco-2 cells 10-fold over control and facilitates the formation of microcolonies (70). Leucine is able to induce LEE4 and LEE5 protein expression similarly to butyrate (69).…”

“…Acetate, propionate, and butyrate increase motility of the Sakai strain (70). Synthesis of the flagellin subunit, FliC, is increased, and the frequency of flagellated bacteria increases upon exposure to these SCFAs.…”