The filamentous cyanobacteria belonging to the genus Trichodesmium represent the major group of N2-fixing planktonic organisms in the ocean [see the review by Capone et al. (Capone et al., 1997)]. Trichodesmium occurs at higher abundances in highly stratified, low-nutrient waters at tropical and subtropical latitudes, often forming smallto large-scale blooms which can be seen from space [e.g. (...

In culture, Azorhizobium caulinodans used at least four terminal oxidases, cytochrome aa3 (cytaa3), cytd, cyto, and a second a-type cytochrome, which together mediated general, respiratory electron (e-) transport to O2. To genetically dissect physiological roles for these various terminal oxidases, corresponding Azorhizobium apocytochrome genes were cloned, and three cytaa3 mutants, a cytd muta...

Dinitrogen (N2) fixation is a major source of bioavailable nitrogen to oligotrophic ocean communities. Yet, we have limited understanding how ongoing climate change could alter N2 fixation. Most our based on short-term laboratory experiments conducted individual N2-fixing species whereas community-level approaches are rare. In this longer-term in situ mesocosm study, aimed improve the role risi...

Biological N2 fixation is achieved under ambient conditions by enzymatic catalysis. The enzyme nitrogenase has been studied extensively, but the N2 chemical reduction step is, by far, not rate limiting and hard to examine. A new method was developed that allows studying the reduction transition state within the enzyme's complex kinetic cascade by means of the 15N kinetic isotope effect on the r...

Biological N2 fixation, the reduction of N2 to NH 3 , is catalyzed by the enzyme nitrogenase . Fractionation studies of nitrogenases from a variety of organisms have shown that all are composed of two similar proteins, one contains Mo and Fe and is called the Mo-Fe protein and the other contains only Fe and is called the Fe protein . Recently homogeneous preparations of these proteins from Azot...

The symbiotic association between Medicago truncatula and Sinorhizobium meliloti is a well-established model system in the legume-Rhizobium community. Despite its wide use, the symbiotic efficiency of this model has been recently questioned and an alternative microsymbiont, S. medicae, has been proposed. However, little is known about the physiological mechanisms behind the higher symbiotic eff...

N2-fixation by Rhizobium-legume symbionts is of major ecological and agricultural importance, responsible for producing a substantial fraction of the biosphere's nitrogen. On the basis of 15N-labelling studies, it had been generally accepted that ammonium is the sole secretion product of N2-fixation by the bacteroid and that the plant is responsible for assimilating it into amino acids. However...

An isolate of the filamentous cyanobacterium Microcoleus sp. was obtained from black mangrove aerial root (pneumatophore) and inoculated onto young mangrove seedlings to evaluate N2-fixation and rootcolonization capacities of the bacterium under in vitro conditions in closed-system experiments. N2 fixation (acetylene reduction) gradually increased with time and reached its peak 5 days after ino...

It is now well established that almost all phases of root nodule development in legumes are adversely affected by saline conditions in the rooting medium. There is also a general agreement that the rhizobia are more tolerant to salt stress than the host plant, but they show considerable strain variability in growth and survival under saline conditions. Inhibitory effect of salinity on nodulatio...

Corals evolved by establishing symbiotic relationships with various microorganisms (the zooxanthellae, filamentous algae, cyanobacteria, bacteria, archaea, fungi and viruses), forming the 'coral holobiont'. Among them, the endolithic community is the least studied. Its main function was considered to be translocation of photo-assimilates to the coral host, particularly during bleaching. Here, w...