Central metabolism controls transcription of a virulence gene regulator in Vibrio cholerae

Abstract

ToxT is the central regulatory protein involved in activation of the main virulence genes in Vibrio cholerae. We have identified transposon insertions in central metabolism genes, whose disruption increases toxT transcription. These disrupted genes encode the primary respiration-linked sodium pump (NADH : ubiquinone oxidoreductase or NQR) and certain tricarboxylic acid (TCA) cycle enzymes. Observations made following stimulation of respiration in the nqr mutant or chemical inhibition of NQR activity in the TCA cycle mutants led to the hypothesis that NQR affects toxT transcription via the TCA cycle. That toxT transcription increased when the growth medium was supplemented with citrate, but decreased with oxaloacetate, focused our attention on the TCA cycle substrate acetyl-CoA and its non-TCA cycle metabolism. Indeed, both the nqr and the TCA cycle mutants increased acetate excretion. A similar correlation between acetate excretion and toxT transcription was observed in a tolC mutant and upon amino acid (NRES) supplementation. As acetate and its tendency to decrease pH exerted no strong effect on toxT transcription, and because disruption of the major acetate excretion pathway increased toxT transcription, we propose that toxT transcription is regulated by either acetyl-CoA or some close derivative. INTRODUCTIONCholera is a severe waterborne diarrhoeal disease that remains a public health concern in many developing countries. The causative agent of cholera is Vibrio cholerae, a Gram-negative bacterium. The two main essential virulence factors of V. cholerae are toxin-coregulated pilus (TCP) and cholera toxin (CT). TCP is a type IV pilus that is required for colonization of the small intestine. CT is a potent enterotoxin responsible for inducing most of the cholera symptoms. The genes that encode TCP, CT and many other virulence determinants comprise a network of genes called the ToxT regulon, whose expression is modulated by a hierarchy of transcriptional regulators (Matson et al., 2007). These regulators include the transcription factors AphA and AphB, which positively regulate transcription of tcpPH. The membrane-bound protein complex TcpPH works with the membrane-bound protein complex ToxRS to activate transcription of toxT, which encodes an AraC-type transcriptional factor (Matson et al., 2007). While it is ToxT that directly activates the genes that encode TCP, CT and the rest of the ToxT regulon, additional positive regulators have been reported. In contrast, our knowledge concerning factors that negatively regulate the ToxT regulon (reviewed by Matson et al., 2007) is restricted to the nucleoid-associated protein H-NS, which represses transcription of toxT, tcpA and ctxAB (Nye et al., 2000;Stonehouse et al., 2011), and the cAMP-receptor protein (CRP), which is reported to negatively regulate tcpPH (Kovacikova & Skorupski, 2001).In a previous attempt to identify negative regulators of toxT transcription, we found that elevated toxT transcription results from loss of the primary respiration-linked sodium pu...

Roles of the Sodium-Translocating NADH:Quinone Oxidoreductase (Na+-NQR) on Vibrio cholerae Metabolism, Motility and Osmotic Stress Resistance

“…We had previously suggested that TCA cycle activity is decreased in the V. cholerae Δ nqrA-F mutant [10]. Consistent with this, intracellular isocitrate levels were decreased in the Δ nqrA-F mutant (Table 3).…”

The Fatty Acid Regulator FadR Influences the Expression of the Virulence Cascade in the El Tor Biotype of Vibrio cholerae by Modulating the Levels of ToxT via Two Different Mechanisms

“…However, FadR clearly regulates the expression of additional genes in V. cholerae and one or more of these may influence the transcription of toxT. Since the toxT promoter is responsive to changes in central metabolism (58), it is also possible that global metabolic changes that occur in the ΔfadR mutant result in altered transcription of ToxT.…”

Role of Indole Production on Virulence of Vibrio cholerae Using Galleria mellonella Larvae Model

“…ions are accumulated inside the cell and electrochemical ion gradient may be enforced to shift and subsequently reduce the virulence and motility of V. cholerae. Accumulation of oxaloacetate itself could result in virulence suppression because this has been reported to inhibit the expression of ToxT, a global regulator of virulence in V. cholerae [39].…”