Contribution
Trichodesmium, the paradoxical diazotroph
Gallon, John R.; Jones, D. Alun; Page, T. Selwyn
Algological Studies/Archiv für Hydrobiologie, Supplement Volumes No. 83 (1996), p. 215 - 243
110 références bibliographiques
publié: Dec 19, 1996
DOI: 10.1127/algol_stud/83/1996/215
ArtNo. ESP142011700016, Prix: 29.00 €
Abstract
The marine cyanobacterium Trichodesmium may contribute as much as 6% to the annual rate of global N2 fixation. Unsually however, Trichodesmium fixes N2 during the day, simultaneously with oxygenic photosynthesis, and does not therefore effect the temporal separation between these two incompatible processes that characterizes other non-heterocystous cyanobacteria that are capable of aerobic N2 fixation. Immunoelectron microscopy suggests that nitrogenase may be confined only to certain cells in a bundle of trichomes and physiological studies are generally consistent with this view. N2-fixing cells may also catalyse photosynthetic electron transport but probably do not evolve O2. Regulation of nitrogenase activity during growth of Trichodesmium under a diurnal pattern of illumination is exerted at the level of nif gene transcription and also by the posttranslational modification of the Fe-protein of nitrogenase. However, additional modulation of N2 fixation in Trichodesmium may follow from the ability of this cyanobacterium to regulate its buoyancy and thereby migrate to different depths within the column of water in which it is suspended.
Mots-clefs
Trichodesmium • cyanobacteria • N2 fixation • nitrogenase • photosynthesis • O2 • diurnal rhythm • buoyancy regulation • gas vesicles • nutrient exchange