Heterocyst Structure Alteration and O2-Mediated Inhibition of Dinitrogen Fixation by Trichlorfon inAnabaenaPCC 7119

The involvement of a primary inhibition of dinitrogen fixation in the toxic effect of trichlorfon in cyanobacteria has been investigated. Significant inhibition of nitrogenase activity can be detected 3 h after the addition of insecticide to batch cultures of Anabaena PCC 7119. Recovery of nitrogenase activity starts between 6–12 h after removal of the insecticide, suggesting a requirement for the induction of new heterocysts. Under anaerobic conditions the inhibitory effect of the insecticide is largely prevented. Biochemical analysis indicates that envelope glycolipids exist in trichlorfon-treated cultures. However, ultrastructural examination shows heterocyst deterioration and the failure of the inner glycolipid layer of the heterocyst envelope. Our data are consistent with the view that destabilization of the heterocyst envelope is the first target of insecticidal action. Inhibition of dinitrogen fixation and growth have also been shown in the cyanobacteria Gloeothece PCC 6501, Nostoc UAM 205, and Chlorogloeopsis PCC 6912.