this compound binds oxygen, and it is synthetized by the plant. The heme is formed
by bacteria of the genus Rhizobium.
According to Cyril A. Appleby (1984), symbiotic oxygen fixation is considered
as an “oxygen paradox.” That means components necessary for the enzymatic
reduction of nitrogen to ammonia are oxygen-labile (sensitive to the action of
oxygen), while the respective microorganisms are obligatorily aerobic and dependent on respiration using oxygen as a terminal acceptor of hydrogen and of electrons
for accomplishing the production of ATP.
8.4.3 Nonsymbiotic Nitrogen Fixation
The amount of nitrogen bound by non-symbiotic fixation in the soil is very small in
comparison with the nitrogen volume fixed by microorganisms living in symbiosis
with leguminous plants. However, non-symbiotic nitrogen fixation is of a great
importance in aqueous environments. Atmospheric nitrogen can also be fixed
without symbiosis by some species of the phylum Cyanobacteria (blue-green
bacteria) and also by the sporogenic genus Clostridium and the genus Beijerinckia.
The Dutch soil microbiologist Martinus Willem Beijerinck (1851–1931) isolated in
1893 an anaerobic spore-producing microorganism and named it Granulobacter
butylicum; its present name is Clostridium butyricum. Two years later, a famous
Russian microbiologist Sergei Winogradsky (1856–1953) described Clostridium
pasteurianum as another nonsymbiotic fixer of atmospheric nitrogen. Yet another
bacterium, Azotobacter chroococcum, one of the most common nitrogen fixers, was
discovered by Beijerinck in 1901. There are some other atmospheric nitrogen-fixing
bacteria, although less efficient ones, for example, bacteria of the genera Bacillus,
Enterobacter, Chromatium, Chlorobium, and Klebsiella.
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by bacteria of the genus Rhizobium.
According to Cyril A. Appleby (1984), symbiotic oxygen fixation is considered
as an “oxygen paradox.” That means components necessary for the enzymatic
reduction of nitrogen to ammonia are oxygen-labile (sensitive to the action of
oxygen), while the respective microorganisms are obligatorily aerobic and dependent on respiration using oxygen as a terminal acceptor of hydrogen and of electrons
for accomplishing the production of ATP.
8.4.3 Nonsymbiotic Nitrogen Fixation
The amount of nitrogen bound by non-symbiotic fixation in the soil is very small in
comparison with the nitrogen volume fixed by microorganisms living in symbiosis
with leguminous plants. However, non-symbiotic nitrogen fixation is of a great
importance in aqueous environments. Atmospheric nitrogen can also be fixed
without symbiosis by some species of the phylum Cyanobacteria (blue-green
bacteria) and also by the sporogenic genus Clostridium and the genus Beijerinckia.
The Dutch soil microbiologist Martinus Willem Beijerinck (1851–1931) isolated in
1893 an anaerobic spore-producing microorganism and named it Granulobacter
butylicum; its present name is Clostridium butyricum. Two years later, a famous
Russian microbiologist Sergei Winogradsky (1856–1953) described Clostridium
pasteurianum as another nonsymbiotic fixer of atmospheric nitrogen. Yet another
bacterium, Azotobacter chroococcum, one of the most common nitrogen fixers, was
discovered by Beijerinck in 1901. There are some other atmospheric nitrogen-fixing
bacteria, although less efficient ones, for example, bacteria of the genera Bacillus,
Enterobacter, Chromatium, Chlorobium, and Klebsiella.
Vladimír Klaban
148
V. Klaban