Microbiology and Nitrogen Cycle

Chemosynthesis occurs only in colourless aerobic bacteria such as, Nitrosomonas, Nitrobacter etc.

Milnesium tardigradum is a tardigrade microorganism that exhibits a high degree of radioresistance.

Spirochetes have periplasmic flagella. They reside inside the cell, within the periplasmic space.

Low temperature Crenarchaeota named Nitrosopumilus maritimus is an ammonia-oxidising organism. It affects the oceanic nitrogen cycle.

Gluconobacter has polar flagella whereas Acetobacter has peritrichous flagella.

Fibrobacteres is a small bacterial phylum which includes many of the major rumen bacteria. They allow the degradation of plant-based cellulose in ruminant animals.

Nanoarchaeum equitans appears to be an obligate symbiont on the archaeon Ignicoccus. It is one of the smallest known cellular organisms and the smallest known archaeon.

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.