Modifiers of heterocyst repression and spacing and formation of heterocysts without nitrogenase in the cyanobacterium Anabaena variabilis

Twelve amino acid analogs and related compounds were screened for their ability to induce heterocysts in ammonia-repressed, undifferential filaments of Anabaena variabilis. As has been previously described, 1-methionine-dl-sulfoximine induces both heterocysts and nitrogenase. In contrast, dl-7-azatryptophan and beta-2-thienyl-dl-alanine were found to induce heterocysts but not nitrogenase activity (measured as acetylene reduction) even under microaerobic conditions. When the initial ammonium concentration was reduced, dl-7-azatryptophan-treated cultures sequentially produced heterocysts and then nitrogenase activity, but nitrogenase was detected only when a parallel culture without analog also became capable of acetylene reduction. Neither of the two latter analogs affected gamma-glutamyl transferase activity in crude extracts. All three analogs significantly reduced the mean interheterocyst distance in nitrogen-fixing cultures.