Several Nitrogen-Fixing Bacteria

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Nitrogen Fixation in Free-Living and Associative Symbiotic Bacteria Nitrogen Fixing Bacteria Nitrogenase Genetics Mechanism of Nitrogen Fixation Response of Plants to Azotobacter Inoculation Nitrogen Fixation in the Root Zone of Rice

Several Nitrogen-Fixing Bacteria

Several nitrogen-fixing bacteria (from Boddey and Dobereiner, 1988)

Nitrogen-fixing bacteria	In association with
Azospirillum lipoferum	Many grasses and cereals such as maize, wheat, sorghum, rice
Azospirillum brasilense	Many grasses and cereals such as maize, wheat, sorghum, rice Rice
Pseudomonas sp.	Rice
Pseudomonas sp.	Deschampsia caespitosa
Campylobacter nitrofigilis	Spartina alterniflora (Salt march grass)
Azospirillum amazonense	Many grasses in Amazon and Brazil
Bacillus azotofixans	Several grasses, wheat, sugarcane
Herbaspirillum seropedicae	Many grasses and cereals (Maize)
Azospirillum halopraeferans	Kallar grass
Azotobacter nitrocaptans	Sugarcane

The question of colonization and mode of entry of these diazotrophs into the root interior remains to be fully answered.

The 2,3,5-triphenyl terrazolium dichloride (TIC) mediated reduction staining of cell contents including live bacteria has been advocated as one way of substantiating the presence of bacteria but this has obvious limitations in pinpointing the authenticity of particular species of a microorganism.

Electron micrographs showing the presence of the bacteria of the genus Campylobacter in the aerenchyma of field grown Spartina alterniflora have been cited as proof of bacterial colonization.

More recently, through microscopic evidence aided by the use of the protein A-gold technique and silver amplification, diazotrophs have been show to predominate the roots of kallar grass (Leptochloa fusca) and wheat.

The technique has revealed that A. brasilense occupy the intercellular spaces of the root cortex. However, the bacterial cells were not detected either in the endodermis or the vascular bundle.

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