Nitrogen fixation is the process by which atmospheric inert nitrogen is converted into ammonia or nitrogen oxide. Bacteria are the component of biological nitrogen fixation; free living non-symbiotic soil bacteria carry out nitrogen fixation. It includes aerobic bacteria (Azotobacter spp), anaerobic bacteria (Clostridium spp), photosynthetic bacteria (Rhodospirillum spp), chemosynthetic bacteria (Thiobacillus spp) and blue green algae.