A potential physiological role for cyanotoxins in cyanobacteria of arid environments

The ecological or physiological function of most cyanotoxins has remained largely unknown despite much speculation and the development of several hypotheses. The possible role of two of these toxins, microcystin and β-N-methylamino-l-alanine (BMAA) within producing organisms is discussed within the context of survival in arid environments and the consequent potential for the presence of such toxins in these environments. Cellular microcystin and BMAA concentrations are modulated by cellular carbon:nitrogen balance which in turn reflects environmental nitrogen availability and light intensity or duration. Both toxins result in decreased photosynthesis. However, available nitrogen relative to light and/or carbon fixation has opposite effects on the concentration of these toxins. We present data to explain this apparent contradiction and to support the role of these toxins in inhibition of photosynthesis. Additionally, we discuss how their different modes of achieving inhibition of photosynthesis may offer a survival advantage to cyanobacteria exposed to rapid changes in photosynthetic activity in arid environments. •Common cyanobacterial toxins are environmentally regulated.•Both BMAA and microcystin play a role in regulating primary metabolism.•Their function appears to be the regulation of photosynthesis as a function of nitrogen availability.•Nitrogen availability in arid environments is determined by N-fixation rate which is, in turn, dependent on adequate water.•BMAA and microcystin are therefore to be expected in cyanobacterial mats from arid environments.