PSP toxin release from the cyanobacterium Raphidiopsis brookii D9 (Nostocales) can be induced by sodium and potassium ions

► We explored the effect of monovalent cations on PSP toxin production in Raphidiopsis brookii D9. ► R. brookii D9 is capable of releasing PSP toxins into the extracellular medium. ► Toxins release occurs in response to the presence of Na+ and K+ ions. ► SxtF/M transport proteins conserve motifs that are implicated in Na+ ion recognition. ► PSP toxins could act extracellularly as a protective mechanism to ensure homeostasis.