THE PRESENCE AND EXPRESSION OF HETR IN THE NONHETEROCYSTOUS CYANOBACTERIUM SYMPLOCA PCC-8002

The filamentous cyanobacteria Symploca PCC 8002 (Symploca) and Trichod esmium spp. fix nitrogen aerobically in the light in a light/dark cycl e, without forming specialized thick-walled cells (heterocysts), Even though they do not form heterocysts, we amplified and sequenced a segm ent of a key regulatory gene in heterocyst differentiation, the hetR g ene, from Symploca, Trichodesmium erythraeum and Leptolyngbya PCC 7311 0 (which fixes nitrogen anaerobically) using degenerate oligonucleotid es. The transcriptional level of hetR in Symploca PCC 8002 was examine d in relation to nifH expression during nitrogen step-down. The expres sion pattern of hetR suggests that it was not induced during removal o f combined nitrogen, as is the case with the heterocystous cyanobacter ia. This is the first report of sequences corresponding to a portion o f hetR from within the group of non-heterocystous cyanobacteria. (C) 1 998 Federation of European Microbiological Societies. Published by Els evier Science B.V. All rights reserved.