Microbiology and Nitrogen Cycle

Escherichia coli is a Gram-negative, facultatively anaerobic, rod-shaped bacterium. The flagella in E. coli have a peritrichous arrangement. Staphylococcus aureus is an atrichous, Gram-positive, sphere-shaped bacteria that form clusters. Vibrio cholerae is a monotrichous, Gram-negative, comma-shaped bacterium.

Aulosira, Anabaena, and Nostoc are all blue-green algae (cyanobacteria) capable of atmospheric nitrogen fixation. They possess nitrogenase enzymes for this purpose. The question correctly identifies that all these genera have nitrogen-fixing capability. Note: 'Anabaea' appears to be a typo for 'Anabaena'.

Rhodospirillum, Rhodopila, and Rhodobacter are all photosynthetic bacteria capable of anoxygenic photosynthesis using bacteriochlorophyll. These purple non-sulfur and purple sulfur bacteria use organic compounds or sulfur compounds as electron donors instead of water.

Escherichia coli (E. coli) is a bacterium that naturally inhabits the human intestinal tract as part of the normal gut microbiota. While it can be found in water and soil due to fecal contamination, its primary habitat is the human intestine where it aids in digestion and vitamin K production.

This is the correct option, as rhizobium bacteria do not live in the stem of legumes such as gram, peas and other pulses. They live in the roots of legumes and provide them with nitrogen. In return, the plants provide food and shelter to the bacteria.

Rhizobium is the most well-known symbiotic nitrogen-fixing bacterium, forming mutualistic associations with legume plants in root nodules. The bacteria convert atmospheric nitrogen into ammonia that the plant can use, while receiving carbohydrates from the plant. Nitrosomonas and Nitrobacter are involved in nitrification, not nitrogen fixation.

Clostridium is a genus of anaerobic, free-living bacteria that includes species capable of fixing atmospheric nitrogen. Unlike Rhizobium (which forms symbiotic relationships with legumes) or Azotobacter (which is aerobic), Clostridium species can fix nitrogen independently in anaerobic conditions. These bacteria play important roles in soil nitrogen cycling, particularly in waterlogged or oxygen-poor environments.

Vibrio is the coma-shaped (curved) bacterium. Coccus is spherical, Bacillus is rod-shaped, and Spirillum is spiral-shaped. The distinctive comma shape is characteristic of Vibrio cholerae.

It is a large, diverse genus of plants with between 200 and 400 species belonging to the daisy family Asteraceae. Asteraceae family is not involved in nitrogen fixation.

Dialister pneumosintes is the smallest bacterium (0.15—0.3 n long). 

Biogas plants rely on methanogenic archaebacteria (archaea) to convert organic matter into methane-rich biogas through anaerobic digestion. Cyanobacteria are photosynthetic, myxobacteria are soil bacteria, and mycobacteria include pathogens like TB - none are involved in biogas production.

The rhizosphere is the narrow region of soil directly influenced by root secretions and associated soil microorganisms. These microorganisms have symbiotic relationships with plants - they help in nutrient absorption, nitrogen fixation, and plant growth promotion in exchange for root exudates as food.

These organisms can utilise energy released during the chemical reaction occurring in them. Sulphur and iron bacteria are chemoautotrophic.

This is the correct asnwer as soil microorganisms and associated plant roots, lightning and cosmic radiation and some marine animals can fix nitrogen from the atmosphere.