DIEL VARIABILITY IN TRANSCRIPTION OF THE STRUCTURAL GENE FOR GLUTAMINE-SYNTHETASE (GLNA) IN NATURAL-POPULATIONS OF THE MARINE DIAZOTROPHIC CYANOBACTERIUM TRICHODESMIUM-THIEBAUTII

A 360-bp fragment of the Trichodesmium thiebautii glutamine synthetase gene (glnA) was amplified from DNA isolated from oceanic populations of this ecologically important, diazotrophic cyanobacterium. The clone d fragment showed high homology to the type 1 glutamine synthetase (GS ) enzymes of other cyanobacteria and was used to probe the in situ, te mporal variability in transcription of Trichodesmium GS. Three distinc t phases in the diel pattern of glnA mRNA abundance were observed. The se appear to be correlated with the temporal variability in carbon and nitrogen fixation rates and the effect that these physiological proce sses have on the size of cellular pools of the primary end-products of N assimilation, Our data show that Trichodesmium thiebautii GS is reg ulated at the level of transcription and support the hypothesis that G S expression in this organism is subject to similar controls as those established for heterocyst-forming cyanobacteria.