Nitrifying bacteria are chemoautotrophs. They gain their energy by chemical oxidations (chemo-) and they are autotrophs (self-feeders) because they do not depend on pre-formed organic matter.

Iron (Fe), molybdenum (Mo) and vanadium (Vd) are present in nitrogenase enzyme.

Dihydrogen acts as a competitive inhibitor of nitrogenase.

Nitrobacter winogradsky oxidises nitrite to nitrate.

Ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) are required for the conversion of ammonia to nitrite.

Species of Pseudomonas, Alkaligenes and Bacillus are involved in the process of denitrification. Their activities result in substantial losses of nitrogen into the atmosphere, roughly balancing the amount of nitrogen fixation that occurs each year.

Martinus Beijerinck (1888) of Holland discovered nitrogen-fixing organisms.

Desulfovibrio is a free-living chemosynthetic N₂ fixer.

Diazotrophs are specific group of prokaryotes involved in the process of nitrogen fixation.

16 moles of ATPs are consumed when 1 mole of nitrogen is fixed. The reaction is as follows: N₂ + 8H+ + 8e^- + 16 ATP = 2NH₃ + H₂ + 16ADP + 16 Pi

Desulfovibrio is a free living anaerobic nitrogen fixer.

Agricultural lands fix the maximum amount of N₂. It fixes about 90 x 10^12 gram per year.

Root nodules of chickpea and some other legumes are formed by small-celled rhizobia termed bradyrhizobium.

Leghaemoglobin is found only in the nodules; leghaemoglobin may regulate the supply of oxygen to the nodule tissues in the same way as haemoglobin regulates the supply of oxygen to mammalian tissues.

This is a correct match. Pea has R. leguminosarum in root nodules, Soya bean has R. japonicum in root nodules, Alfalfa has R. melioti in root nodules and Urad has R. phaseoli in root nodules.