Effects of Saxitoxin (STX) and Veratridine on Bacterial Na+-K+ Fluxes: a Prokaryote-Based STX Bioassay

Università degli Studi dell'Insubria, Varese, Lombardy, Italy
Applied and Environmental Microbiology (Impact Factor: 3.67). 01/2004; 69(12):7371-6. DOI: 10.1128/AEM.69.12.7371-7376.2003
Source: PubMed


Saxitoxin (STX) is a potent natural sodium channel blocker and represents a significant health concern worldwide. We describe here the antagonistic effects of STX and veratridine (VTD), an Na+ channel activator, on three gram-negative bacteria and their application to an STX bioassay. STX reduced the total cellular levels of both Na+ and K+, as measured by flame photometry, whereas VTD increased the cellular concentrations relative to control ion fluxes in the cyanobacterium Cylindrospermopsis raciborskii AWT205. Endogenous STX production in toxic cyanobacterial strains of C. raciborskii and Anabaena circinalis prevented cell lysis induced by VTD stress. Microscopic cell counts showed that non-STX producing cyanobacteria displayed complete cell lysis and trichome fragmentation 5 to 8 h after addition of VTD and vanadate (VAN), an inhibitor of sodium pumps. The addition of STX, or its analogue neoSTX, prior to treatment with VTD plus VAN prevented complete lysis in non-STX-producing cyanobacteria. VTD also affected cyanobacterial metabolism, and the presence of exogenous STX in the sample also ameliorated this decrease in metabolic activity, as measured by the cellular conversion of tetrazolium into formazan. Reduced primary metabolism was also recorded as a decrease in the light emissions of Vibrio fischeri exposed to VTD. Addition of STX prior to VTD resulted in a rapid and dose-dependent response to the presence of the channel blocker, with samples exhibiting resistance to the VTD effect. Our findings demonstrate that STX and VTD influence bacterial Na+ and K+ fluxes in opposite ways, and these principles can be applied to the development of a prokaryote-based STX bioassay.

Download full-text


Available from: Brett A Neilan, Jan 13, 2015
  • Source
    • "Futhermore, both Na + and K + levels were found to affect STX localisation in Raphidiopsis brookii D9 (Soto-Liebe et al., 2012). In addition, STX has been shown to inhibit cellular uptake of Na + in C. raciborskii AWT205, a non PSP-producing species of cyanobacteria, via perturbation of Na + /K + ion channels in a manner antagonistic of the Na + channel activator veratridine (Pomati et al., 2003a). "
    [Show abstract] [Hide abstract]
    ABSTRACT: Saxitoxins (STX), neurotoxic alkaloids, fall under the umbrella of Paralytic Shellfish Toxins (PSTs) produced by marine dinoflagellates and freshwater cyanobacteria. The genes responsible for the production of saxitoxin have been proposed, but factors that influence their expression and induce toxin efflux remain unclear. Here we characterise the putative STX NorM-like MATE transporters SxtF and SxtM. Complementation of the antibiotic-sensitive strain Escherichia coli KAM32 with these transporters decreased fluoroquinolone sensitivity indicating that, while becoming evolutionary specialised for STX transport, these transporters retain relaxed specificity typical of this class. The transcriptional response of STX biosynthesis (sxtA) along with that of the STX transporters (sxtM and sxtF from Cylindrospermopsis raciborskii T3, and sxtM from Anabaena circinalis AWQC131C) were assessed in response to ionic stress. This data, coupled with a measure of toxin intracellular to extracellular ratios provides an insight into the physiology of STX export. C. raciborskii and A. circinalis exhibited opposing responses under conditions of ionic stress. High Na+ (10 mM) induced moderate alterations of transcription and STX localisation, whereas high pH (pH 9) stimulated the greatest physiological response. STX production and cellular localisation is responsive to ionic strength indicating a role of this molecule in the maintenance of cellular homeostasis.
    Full-text · Article · Sep 2015 · Environmental Microbiology
  • Source
    • "Saxitoxin is a neuronal Na 1 channel blocker that inhibits axonal impulse conduction in most populations of enteric neurons at low (o 1 mmol L À1 ) concentrations. At higher concentrations (4 1 mmol L À1 ), it has been found to alter Escherichia coli chemotaxis (Tisa et al., 2000) and cation fluxes in cyanobacteria as well (Pomati et al., 2003). The recovery of Salmonella Typhimurium from Peyer's patches treated with saxitoxin was decreased relative to tissues untreated with the toxin. "
    [Show abstract] [Hide abstract]
    ABSTRACT: Peyer's patches of the small intestine serve as inductive sites for mucosal immunity as well as targets for invasive enteropathogens, including Salmonella. Because they are innervated by catecholamine-containing enteric nerves, the hypothesis that the endogenous catecholamines dopamine and norepinephrine or sympathomimetic drugs alter Salmonella Typhimurium uptake into Peyer's patches was tested. Porcine jejunal Peyer's patch explants were mounted in Ussing chambers and inoculated with a porcine field isolate of Salmonella Typhimurium DT104. Salmonella recovery from gentamicin-treated tissues increased significantly between 30 and 90 min of bacterial exposure to the mucosal surface. Addition of the neuronal conduction blocker saxitoxin (0.1 micromol L(-1)) or dopamine (30 micromol L(-1)) to the contraluminal aspect of explants decreased bacterial recovery after 60 min of Salmonella exposure. The effects of dopamine were mimicked by cocaine and methamphetamine (30 micromol L(-1)), which act on catecholaminergic nerve terminals to increase synaptic neurotransmitter concentrations. These results suggest that enteric catecholaminergic nerves modulate Salmonella colonization of Peyer's patches at the earliest stages of infection, in part by altering epithelial uptake of bacteria.
    Preview · Article · Feb 2008 · FEMS Immunology & Medical Microbiology
  • Source

    Full-text · Article ·
Show more