Some New Nitrogen-fixing Bacterial Associations

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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

Some New Nitrogen-fixing Bacterial Associations

	Some New Nitrogen-fixing Bacterial Associations As stated earlier, the genus Azospirillum appears to be widespread in the roots of many graminaceous species. A. amazonens is an acid tolerant and sucrose utilizing species isolated from the root system of sugarcane and sweet sorghum. In Pakistan, salt affected. soils abound in Kallar grass (Leptochloa fusca) on whose root surfaces Azospirillum halopraeferans has adapted its existence to the harsh ecological surroundings with optimum requirement of 41"C and 0.25 per cent salt concentrations.
A bacterium named Herbaspirillum seropedicae has been isolated from washed and surface sterilized roots of maize, rice and sorghum in Rio de Janeiro.The bacterium has bipolar flagella and N₂ fixation is more O₂ and pH tolerant than that of azospirilla. At the International Rice Research Institute, Philippines, a bacterium named as Pseudomonas diazotrophicus has been isolated from roots of rice and weeds in low land rice growing tracts but not from upland rice regions. A new species of Campylobacter (McClung and Patriquin, 1980) has been reported to occur in the roots of a water weed (Spartina alterniflora), which appears to be very sensitive to oxygen.
A strain of Bacillus azotofixans capable of fixing nitrogen efficiently was isolated from surface sterilized roots of grasses, wheat and sugarcane which, 'like Azotobacter paspali isolated from the roots of paspalum grass, is also nitrate dependent for growth and capable of fixing nitrogen in the presence of combined nitrogen. The residual sugar in sugar in sugarcane in many parts of Brazil contain Azotobacter nitrocaptans in the range of 103 to 107 per g wet weight basis.
This nitrogen-fixing species appears to grow well in 10 per cent sugar or 1 per cent cane juice, acidified with acetic acid to pH 4.5.It is a small Gram-negative aerobic bacillus and can use ethyl alcohol for growth. Some plant associated nitrogen-fixing bacteria which have been investigated since 1974.

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