Modulation of gap-junctional intercellular communication by a series of cyanobacterial samples from nature and laboratory cultures

► Extracts and exudates of cyanobacteria inhibited gap-junctional intercellular communication. ► The effects were caused by chemicals different from microcystin and cylindrospermopsin. ► These results indicate an existence of novel tumor promoting cyanotoxins. ► The effects were induced by common bloom-forming cyanobacteria. ► The effects were species- and strain-specific.