Effect of Nitrogen on Cellular Production and Release of the Neurotoxin Anatoxin-A in a Nitrogen-Fixing Cyanobacterium

Alexis Gagnon,Frances R Pick

doi:10.3389/fmicb.2012.00211

Abstract

Anatoxin-a (ANTX) is a neurotoxin produced by several freshwater cyanobacteria and implicated in lethal poisonings of domesticated animals and wildlife. The factors leading to its production in nature and in culture are not well understood. Resource availability may influence its cellular production as suggested by the carbon-nutrient hypothesis, which links the amount of secondary metabolites produced by plants or microbes to the relative abundance of nutrients. We tested the effects of nitrogen supply (as 1, 5, and 100% N of standard cyanobacterial medium corresponding to 15, 75, and 1500 mg L−1 of NaNO3 respectively) on ANTX production and release in a toxic strain of the planktonic cyanobacterium Aphanizomenon issatschenkoi (Nostocales). We hypothesized that nitrogen deficiency might constrain the production of ANTX. However, the total concentration and more significantly the cellular content of anatoxin-a peaked (max. 146 μg/L and 1683 μg g−1 dry weight) at intermediate levels of nitrogen supply when N-deficiency was evident based on phycocyanin to chlorophyll a and carbon to nitrogen ratios. The results suggest that the cellular production of anatoxin-a may be stimulated by moderate nitrogen stress. Maximal cellular contents of other cyanotoxins have recently been reported under severe stress conditions in another Nostocales species.

Highlights

Many cyanobacteria are capable of producing compounds that are toxic to other organisms
A potent neurotoxin synthesized by freshwater cyanobacteria is anatoxin-a (ANTX), likely one of the smallest toxic alkaloids described to date (LD50 of 0.2 mg/kg IP in mice, Carmichael et al, 1979)
ANTX has been detected in lakes and rivers throughout the world (e.g., Codd et al, 2005; Cadel-Six et al, 2007; Wood et al, 2007; Aráoz et al, 2008), and, in some cases, at concentrations leading to lethal poisonings of livestock, domestic animals, and wildlife

Summary

Introduction

Many cyanobacteria are capable of producing compounds that are toxic to other organisms. In addition to the hepatoxins, cytotoxins, and gastrointestinal toxins, there are several types of neurotoxins (Codd et al, 2005). A potent neurotoxin synthesized by freshwater cyanobacteria is anatoxin-a (ANTX), likely one of the smallest toxic alkaloids described to date (LD50 of 0.2 mg/kg IP in mice, Carmichael et al, 1979). Prior to its chemical identification, ANTX was labeled the Very Fast Death Factor due to its ability to induce death within 4 min following intraperitonial injection in mice. ANTX has been detected in lakes and rivers throughout the world (e.g., Codd et al, 2005; Cadel-Six et al, 2007; Wood et al, 2007; Aráoz et al, 2008), and, in some cases, at concentrations leading to lethal poisonings of livestock, domestic animals, and wildlife

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