Regulation of nitrogen fixation in heterocyst-forming cyanobacteria

Böhme, Herbert

doi:10.1016/s1360-1385(98)01290-4

Cited by 111 publications

(81 citation statements)

References 42 publications

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“…In some filamentous cyanobacteria, nitrogen-fixing heterocysts are formed. These heterocysts are terminally differentiated cells with thick cell walls whose interior becomes nearly anaerobic, mainly as a consequence of respiration, allowing the oxygen-sensitive process of nitrogen fixation to continue (31). Nitrogenase is highly sensitive to dioxygen and is irreversibly inactivated by it.…”

Section: Discussionmentioning

confidence: 99%

The Iron Superoxide Dismutase from the Filamentous Cyanobacterium Nostoc PCC 7120

Regelsberger

Laaha

Dietmann

et al. 2004

Journal of Biological Chemistry

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The nitrogen-fixing filamentous cyanobacterium Nostoc PCC 7120 (formerly named Anabaena PCC 7120) possesses two genes for superoxide dismutase, a unique membrane-associated manganese superoxide dismutase (MnSOD) and a soluble iron superoxide dismutase (FeSOD). A phylogenetic analysis of FeSODs shows that cyanobacterial enzymes form a well separated cluster with filamentous species found in one subcluster and unicellular species in the other. Activity staining, inhibition patterns, and immunogold labeling show that FeSOD is localized in the cytosol of vegetative cells and heterocysts (nitrogenase containing specialized cells formed during nitrogen-limiting conditions). The recombinant Nostoc FeSOD is a homodimeric, acidic enzyme exhibiting the characteristic iron peak at 350 nm in its ferric state, an almost 100% occupancy of iron per subunit, a specific activity using the ferricytochrome assay of (2040 ؎ 90) units mg ؊1 at pH 7.8, and a dissociation constant K d of the azide-FeSOD complex of 2.1 mM. Using stopped flow spectroscopy it was shown that the decay of superoxide in the presence of various FeSOD concentrations is first-order in enzyme concentration allowing the calculation of the catalytic rate constants, which increase with decreasing pH: 5.3 ؋ 10 9 M ؊1 s ؊1 (pH 7) to 4.8 ؋ 10 6 M ؊1 s ؊1 (pH 10). FeSOD and MnSOD complement each other to keep the superoxide level low in Nostoc PCC 7120, which is discussed with respect to the fact that Nostoc PCC 7120 exhibits oxygenic photosynthesis and oxygen-dependent respiration within a single prokaryotic cell and also has the ability to form differentiated cells under nitrogen-limiting conditions.

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Section: Discussionmentioning

confidence: 99%

The Iron Superoxide Dismutase from the Filamentous Cyanobacterium Nostoc PCC 7120

Regelsberger

Laaha

Dietmann

et al. 2004

Journal of Biological Chemistry

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“…Cyanobacteria, a group of prokaryotic, photosynthetic nitrogen fixers are present in every ecological niche and therefore, exposed to the toxic effects of the metals. The effects of a few metals have been studied with respect to growth, nitrogenase activity and carbon fixation, (Ting et al1990;Cano et al 1993;Gambrell, 1994;Blackwell et al 1995;Chuan and Liu, 1996;James, 1996;Bohme, 1998;Kimbrough et al 1999;Zaccaro et al 1999;Barman et al 2000;Kisku et al 2000;Kotas and Stasicka, 2000;Suresh Babu et al 2000;Armienta et al 2001;Epniewska and Bucior, 2001;Suresh Babu et al 2001). What has not been attempted is the study of naturally immobilized cyanobacteria such as Aulosira fertilissima, in ameliorating toxicity using similar immobilized conditions in the laboratory.…”

Section: * Corresponding Authormentioning

confidence: 99%

Scavenging of nickel and chromium toxicity in Aulosira fertilissima by immobilization: Effect on nitrogen assimilating enzymes

Banerjee¹,

Mishra²,

Chatterjee³

2004

Electro Journal of Biotech

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The ubiquity of heavy metals in the biosphere results in the introduction of high amounts of toxic metals into the food chain from various sources. In the present study, one of the strongest nitrogen fixing cyanobacterium of the rice fields, Aulosira fertilissima, was subjected to nickel and chromium stress and the ameliorating effect of immobilization was investigated. Cell immobilization could protect the organism's growth against the toxicity of both heavy metals at LC 50 as compared to lethal concentrations. The nitrate reductase activity in free cells treated with the metals was substantially inhibited but immobilized cells treated with 0.1 ppm nickel was not affected by the metal treatment. Cell immobilization also resulted in a significant protection against sublethal concentration of chromium but to a lesser degree than it did with sub-lethal levels of nickel. Control immobilized cells also had higher Nitrogenase activity than control free cells. Nickel and chromium addition markedly decreased the enzyme activity in free cells but immobilized cells exposed to sublethal concentrations of both metals could overcome this decrease. Glutamine synthetase showed similar response under immobilized conditions compared to free cells with both metals. The addition of algal filtrate in 3:1 ratio further increased the nitrogenase activity compared with immobilized cells treated with sublethal doses of both metals. Immobilization facilitated higher uptake of nickel as compared to chromium. The observations of the present study clearly demonstrate the protective effect of immobilization on Aulosira fertilissima against Nickel and chromium toxicity. Rice field ecosystem thus possess a bidirectional natural metal ameliorating system where Aulosira mats act as a naturally immobilized system and the decay of Aulosira along with other cyanobacteria act as natural chelators protecting the rice plants from deleterious effects of the heavy metals. Most importantly is that the immobilization process protects the cyanobacterial nitrogen fixing process allowing it to maintain nitrogen economy of the fields in spite of the presence of heavy metals.Heavy metals are ubiquitous in the biosphere where they

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“…Triose phosphates, if not directly imported from vegetative cells, can be removed from the oxidative pentose phosphate cycle and converted to pyruvate via the Entner-Doudoroff pathway. Pyruvate is required for generation of reductant for nitrogenase under iron-limiting growth conditions, and to generate acetyl-CoA for synthesis of fatty acids and Hgl (Bo¨hme, 1998).…”

Section: Regeneration Of Reductants and Atp In Heterocystsmentioning

confidence: 99%