GROWTH AND NITROGEN-FIXATION OF THE DIAZOTROPHIC FILAMENTOUS NONHETEROCYSTOUS CYANOBACTERIUM TRICHODESMIUM SP IMS-101 IN DEFINED MEDIA - EVIDENCE FOR A CIRCADIAN-RHYTHM

Trichodesmium sp. IMS 101, originally isolated from coastal western At lantic waters by Prufert-Bebout and colleagues and maintained in seawa ter-based media, was successfully cultivated in two artificial media. Its characteristics of growth, nitrogen fixation, and regulation of ni trogen fixation were compared to those of natural populations and Tric hodesmium sp. NIBB 1067. Results indicate that the culture grown in ar tificial media had nitrogen fixation characteristics similar to those when the culture is grown in seawater-based medium and to those of Tri chodesmium sp. in the natural habitat. The study provides practical ar tificial media to facilitate the physiological studies of these import ant diazotrophic cyanobacteria, as well as the cultivation of other Tr ichodesmium species in future studies. Manipulations of the light/dark cycle were performed to determine whether or not the daily cycle of n itrogen fixation is a circadian rhythm. Cultures grown under continuou s light maintained the cycle for up to 6 days. We demonstrated that th e daily cycle of nitrogen fixation in Trichodesmium sp. IMS 101 was at least partially under the control of a circadian rhythm.