Unicellular, diazotrophic cyanobacteria temporally separate dinitrogen (N2) fixation and photosynthesis to prevent inactivation of the nitrogenase by oxygen. This temporal segregation is regulated by a circadian clock with oscillating activities of N2 fixation in the dark and photosynthesis in the light. On the population level, this separation is not always complete, since the two processes ca...

Significant advances in the ecology, physiology and genetics of reductively dechlorinating bacteria have revealed their important environmental roles in bioremediation and in the global chlorine cycle. N2 fixation has been widely observed in symbiotic, associative and free-living bacteria. Here we show physiological and molecular evidence that reductively dechlorinating bacteria are capable of ...

Dinitrogen (N2) fixation (the reduction of atmospheric N2 to ammonium by specialized prokaryotic microbes), represents an important input of fixed nitrogen and contributes significantly to primary productivity in the oceans. Marine N2 fixation was discovered in the North Atlantic Ocean (NA) in the 1960s. Ever since, the NA has been subject to numerous studies that have looked into the diversity...

Bryophyte establishment represents a positive feedback process that enhances soil development in newly exposed terrain. Further, biological nitrogen (N) fixation by cyanobacteria in association with mosses can be an important supply of N to terrestrial ecosystems, however the role of these associations during post-glacial primary succession is not yet fully understood. Here, we analyzed chronos...

Cyanobacteria are phototrophic bacteria carrying out oxygen-producing photosynthesis. Indeed, cyanobacteria were the inventors of oxygenic photosynthesis carried out by eukaryotic algae and plants. Besides showing the capability of building their cellular carbon from carbon dioxide, available in the atmosphere, several strains of cyanobacteria have also acquired the ability to fix molecular din...

In the modern ocean, a significant amount of nitrogen fixation is attributed to filamentous, nonheterocystous cyanobacteria of the genus Trichodesmium. In these organisms, nitrogen fixation is confined to the photoperiod and occurs simultaneously with oxygenic photosynthesis. Nitrogenase, the enzyme responsible for biological N2 fixation, is irreversibly inhibited by oxygen in vitro. How nitrog...

Geochemical estimates of N2 fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the as...

[1] In this paper we use a biological-physical model with an explicit representation of Trichodesmium to examine the influence of N2 fixation in the Atlantic. Three solutions are examined, one where the N2 fixation rate has been set to observed levels, one where the rate has been increased to levels comparable to geochemical estimates, and one with no N2 fixation. All solutions are tuned to rep...

[1] Climatological satellite observations in the tropical North Atlantic generally show a wintertime surface chlorophyll-a (Chl-a) maximum except over a broad region in the western North Atlantic that has a summer Chl-a maximum. This region also shows decoupling between Chl-a and vertical nutrient flux, based on the positive relationship between sea surface height anomaly (SSH), sea surface tem...

In 1937, Wilson and Umbreit1 reported that H2 inhibited N2 fixation in red clover plants and when this inhibition proved to be competitive, it implied that N2 and H2 were bound at the same site on the enzyme. The enzyme also binds CO2 and N20' competitively with N2. The first evidence that any compound other than N2 bound at the N2-fixing site could be reduced was supplied when Mozen and Burris...