containing sugar as a source of carbon. Although at the very beginning the bacterium
was quite rare in the medium, it started to fix nitrogen from the atmosphere and used
the nitrogen to synthetize cell proteins, while other microbes did not possess this
ability. That is why Azotobacter multiplied considerably so that it eventually became
a dominant microorganism in the culture. Another species, Azotobacter vinelandii,
can be used for the production of alginate. Alginate is a polysaccharide containing
D-mannuronic acid, which is derived from mannose, and D-guluronic acid which is
a derivative of aldohexose gulose. It also synthetizes pigment called azotochelin. It
belongs to the group of bacteria called Gammaproteobacteria. Research indicated
that siderophores of this bacterium can bind metals other than iron. Overall, the
genus Azotobacter contains seven species, two of which were presented here. The
other four are as follows: Azotobacter armeniacus (isolated in 1984), A. beijerinckii
(isolated in 1904), A. nigricans (isolated in 1949), and A. salinestris (isolated in
1991). There also is a related organism named Azorhizophilus paspali discovered in
1966. The species name “paspali” is derived from the genus Paspalum, a tropical
plant. Azorhizophilus paspali colonizes the rhizosphere and forms elongated rods.
Almost all species of the genus Azotobacter live freely in the soil, and during the
stationary phase of their growth, they display an ovoid shape. They differ among
themselves in their morphology, mobility, and their tolerance to NaCl (so-called
halotolerance), as well as in colony pigmentation. Bacteria of the species Azotobacter fix approximately 10 mg of molecular nitrogen N 2 per 1 g of the carbon source
used. In addition to Azotobacter, genera Beijerinckia and Derxia also fix N 2 under
aerobic conditions. These species are more common in the soils of subtropical and
tropical regions.
8.4.1 Ecology and Development Cycle of the Genus
Azotobacter
In the exponential phase of their growth, all the species of the genus Azotobacter
display a rod-like morphology, and only after their transition into the stationary
phase do they assume an ovoid or a cocoid shape. Often they exist in pairs or in short
chains. They have glutinous colonies, dark-brown in color. Among their characteristics is a formation of exopolysaccharides. They require the trace elements molybdenum or vanadium which function as cofactors of the enzyme nitrogenase.
Azotobacter is common in mild climate regions and can be found in both terrestrial
and aquatic environments. In the polar regions, Azotobacter is very sparse although
it was isolated even in a tundra and tolerates a soil temperature of 0
C. Azotobacter
chroococcum tolerates salts in the soil, while other species do not, and therefore the
other Azotobacter species do not colonize salty soils. Species of the genus Azotobacter are known for their simple form of differentiation, because their vegetative
cells only form cysts. Encystation mostly occurs in older cells at the end of the
exponential phase of growth, when carbon sources in the surrounding environment
146
V. Klaban
was quite rare in the medium, it started to fix nitrogen from the atmosphere and used
the nitrogen to synthetize cell proteins, while other microbes did not possess this
ability. That is why Azotobacter multiplied considerably so that it eventually became
a dominant microorganism in the culture. Another species, Azotobacter vinelandii,
can be used for the production of alginate. Alginate is a polysaccharide containing
D-mannuronic acid, which is derived from mannose, and D-guluronic acid which is
a derivative of aldohexose gulose. It also synthetizes pigment called azotochelin. It
belongs to the group of bacteria called Gammaproteobacteria. Research indicated
that siderophores of this bacterium can bind metals other than iron. Overall, the
genus Azotobacter contains seven species, two of which were presented here. The
other four are as follows: Azotobacter armeniacus (isolated in 1984), A. beijerinckii
(isolated in 1904), A. nigricans (isolated in 1949), and A. salinestris (isolated in
1991). There also is a related organism named Azorhizophilus paspali discovered in
1966. The species name “paspali” is derived from the genus Paspalum, a tropical
plant. Azorhizophilus paspali colonizes the rhizosphere and forms elongated rods.
Almost all species of the genus Azotobacter live freely in the soil, and during the
stationary phase of their growth, they display an ovoid shape. They differ among
themselves in their morphology, mobility, and their tolerance to NaCl (so-called
halotolerance), as well as in colony pigmentation. Bacteria of the species Azotobacter fix approximately 10 mg of molecular nitrogen N 2 per 1 g of the carbon source
used. In addition to Azotobacter, genera Beijerinckia and Derxia also fix N 2 under
aerobic conditions. These species are more common in the soils of subtropical and
tropical regions.
8.4.1 Ecology and Development Cycle of the Genus
Azotobacter
In the exponential phase of their growth, all the species of the genus Azotobacter
display a rod-like morphology, and only after their transition into the stationary
phase do they assume an ovoid or a cocoid shape. Often they exist in pairs or in short
chains. They have glutinous colonies, dark-brown in color. Among their characteristics is a formation of exopolysaccharides. They require the trace elements molybdenum or vanadium which function as cofactors of the enzyme nitrogenase.
Azotobacter is common in mild climate regions and can be found in both terrestrial
and aquatic environments. In the polar regions, Azotobacter is very sparse although
it was isolated even in a tundra and tolerates a soil temperature of 0
C. Azotobacter
chroococcum tolerates salts in the soil, while other species do not, and therefore the
other Azotobacter species do not colonize salty soils. Species of the genus Azotobacter are known for their simple form of differentiation, because their vegetative
cells only form cysts. Encystation mostly occurs in older cells at the end of the
exponential phase of growth, when carbon sources in the surrounding environment
146
V. Klaban