Nitrogen Fixation and Hydrogen Metabolism in Cyanobacteria

Abstract

SUMMARY This review summarizes recent aspects of (di)nitrogen fixation and (di)hydrogen metabolism, with emphasis on cyanobacteria. These organisms possess several types of the enzyme complexes catalyzing N2 fixation and/or H2 formation or oxidation, namely, two Mo nitrogenases, a V nitrogenase, and two hydrogenases. The two cyanobacterial Ni hydrogenases are differentiated as either uptake or bidirectional hydrogenases. The different forms of both the nitrogenases and hydrogenases are encoded by different sets of genes, and their organization on the chromosome can vary from one cyanobacterium to another. Factors regulating the expression of these genes are emerging from recent studies. New ideas on the potential physiological and ecological roles of nitrogenases and hydrogenases are presented. There is a renewed interest in exploiting cyanobacteria in solar energy conversion programs to generate H2 as a source of combustible energy. To enhance the rates of H2 production, the emphasis perhaps needs not to be on more efficient hydrogenases and nitrogenases or on the transfer of foreign enzymes into cyanobacteria. A likely better strategy is to exploit the use of radiant solar energy by the photosynthetic electron transport system to enhance the rates of H2 formation and so improve the chances of utilizing cyanobacteria as a source for the generation of clean energy.

Photoautotrophic hydrogen production by eukaryotic microalgae under aerobic conditions

“…This reaction is catalysed by [FeFe]-H 2 ase, which is extremely sensitive to oxygen and does not require any extra energy in the form of ATP 10 . In the meantime, cyanobacteria may produce hydrogen either as a byproduct of nitrogen fixation using nitrogenase 11 or by a reversible NAD(P)H-dependent NiFe-H 2 ase 12 .…”

Genetic Engineering of Cyanobacteria to Enhance Biohydrogen Production from Sunlight and Water

“…Photobiological production of H 2 by cyanobacteria and eukaryotic microalgae that use H 2 O as the electron donor has the potential to produce renewable clean energy on a scale sufficient to meet much of the world energy demand (Ghirardi et al 2007(Ghirardi et al , 2009Sakurai and Masukawa 2007;Tamagnini et al 2007;Bothe et al 2010;Ghirardi and Mohanty 2010). In cyanobacteria, H 2 gas is generated by either hydrogenase or nitrogenase (Tamagnini et al 2002(Tamagnini et al , 2007.…”

Nitrogen fixing cyanobacteria: their diversity, ecology and utilisation with special reference to rice cultivation

“…In an extensive review article Bothe et al (2010b) have reported more recent information on the mechanisms of N 2 fixation and H 2 metabolism in cyanobacteria including their genetic regulation. According to this article the pattern of pyruvate degradation, ammonium and H 2 formation by nitrogenase, and H 2 uptake by hydrogenases is not only typical of strict and facultative anaerobic bacteria, but also proceeds in cyanobacteria.…”

“…This cluster accepts reducing equivalents from the electron carriers and also binds MgATP/MgADP. The overall reaction of the reduction of one molecule of nitrogen to produce two molecules of ammonia can be depicted by the following equation from Bothe et al (2010b). …”

“…Before nitrogenase can be expressed in cyanobacteria a gene rearrangement has to occur within the nifD (Bothe et al, 2010b). A 11-kb DNA element is excised by a specific enzyme XisA and the two fractions of nifD are ligated to permit nitrogenase transcript formation.…”