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

School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney 2052, New South Wales, Australia.
Applied and Environmental Microbiology (Impact Factor: 3.95). 01/2004; 69(12):7371-6. DOI: 10.1128/AEM.69.12.7371-7376.2003
Source: PubMed

ABSTRACT 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.

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    • "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. "
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