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 NaNO(3) 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.