Which one of the following is not a nitrogen-fixing organism ?

Options

A. Anabaena
B. Nostoc
C. Azotobacter
D. Pseudomonas

Answer

D

Explanation

Pseudomonas is a dentrifying bacteria, which convert ammonia and nitrates into free nitrigen, i.e., these denitrifying bacteria are responsible to liberate free nitrogen in the environment through nitrogen in the environment through nitrogen cycle. Other options (a), (b) and (c) show nitrogen fixing organisms. Azospirillum and Azotobacter are free-living bacteria which absorb free nitrogen from soil, air and convert it into salts of nitrogen like amino acids and entich soil nutrients. Cyanobacteria are autotrophic microbes widely distribued in aquatic and terrestrial environments, many of which can fix atmospheric nitrigen, e.g., Nostoc, Anabaena, Oscillatoria, etc.