GROWTH AND NITROGEN FIXATION OF THE DIAZOTROPHIC FILAMENTOUS NONHETEROCYSTOUS CYANOBACTERIUM TRICHODESMIUM SP. IMS 101 IN DEFINED MEDIA: EVIDENCE FOR A CIRCADIAN RHYTHM1

Abstract

ABSTRACT Trichodesmium sp. IMS 101, originally isolated from coastal western Atlantic waters by Prufert‐Bebout and colleagues and maintained in seawater‐based media, was successfully cultivated in two artificial media. Its characteristics of growth, nitrogen fixation, and regulation of nitrogen fixation were compared to those of natural populations and Trichodesmium sp. NIBB 1067. Results indicate that the culture grown in artificial media had nitrogen fixation characteristics similar to those when the culture is grown in seawater‐based medium and to those of Trichodesmium sp. in the natural habitat. The study provides practical artificial media to facilitate the physiological studies of these important diazotrophic cyanobacteria, as well as the cultivation of other Trichodesmium species in future studies. Manipulations of the light/dark cycle were performed to determine whether or not the daily cycle of nitrogen fixation is a circadian rhythm. Cultures grown under continuous light maintained the cycle for up to 6 days. We demonstrated that the daily cycle of nitrogen fixation in Trichodesmium sp. IMS 101 was at least partially under the control of a circardian rhythm.