Microbiology and Nitrogen Cycle

Rhizobium is a well-known nitrogen-fixing bacterium that forms symbiotic relationships with legume plants, converting atmospheric nitrogen into ammonia in root nodules. The question misspells it as 'Rhozobium', but this is clearly the intended answer. Acetobacter produces acetic acid, Mycoplasma lacks a cell wall, and Chlamydia is an intracellular pathogen - none fix nitrogen.

Spirogyra does not have the ability to fix nitrogen from the atmosphere.

Rhizobium forms a symbiotic relationship with legume roots, converting atmospheric nitrogen into ammonia through nitrogen fixation. This occurs in specialized root structures called nodules. Azotobacter is a free-living nitrogen fixer, while Nitrobacter and Nitrosomonas are involved in nitrification, not nitrogen fixation.

Starfish breathe by absorbing oxygen from special finger-like structures that are found on their body surface. They contain fuzzy patches which perform the same function of gills. Each one of those patches can contain dozens of papulae which are extended when the animal is comfortable and feels secure. Each of these permits the animal to collect oxygen for the starfish to breathe. They are generally found only on the top and side surfaces, generally not on the underside.

The bacteria Nitrosomonas brings about the conversion of ammonia to nitrite. 

Heterocysts refer to the specialized cells found in certain filamentous blue green algae that are capable of fixing atmospheric nitrogen.

There are 3 chemoautotrophs viz. Nitrosomonas, Nitrosococcus and Nitrobacter.

The methanogens oxidizes H₂ as a sole source of energy while transferring the electrons from H₂ to CO₂ in its reduction to methane. Iron bacteria oxidize Fe^₊₊ as energy source to Fe⁺⁺⁺.

Very few gram-positive bacteria have ability to oxidize glucose by Entner–Doudoroff pathway. Enterococcus faecalis is an example of gram-positive bacteria having ability to oxidize glucose by Entner–Doudoroff pathway.

In dissimilative sulfur reduction, elemental sulfur is reduced to hydrogen sulfide. Dissimilative sulfur reducers reduce elemental sulfur to hydrogen sulfide. Campylobacter and Desulfuromonas are dissimilative sulfur reducers.

Desulfobacter uses CO₂ from reverse TCA cycle as major C-Source.

Barophiles (piezophiles or barophilic bacteria) are bacteria which grow preferentially or exclusively at moderately high hydrostatic pressures. Examples: Photobacterium profundum, Schewenella benthica, Colwellia psychrerythraea

Psychrophiles would be expected to grow at refrigeration temperatures. Psychrophiles grow at 0°C and has an optimum growth temperature of 15°C or lower.

Methanopyrus is a rod-shaped hyperthermophilic methanogen, discovered on the wall of a black smoker from the Gulf of California at a depth of 2000 m, at temperatures of 84–110 °C. Pyrodictium is a genus of submarine hyperthermophilic archaea whose optimal growth temperature ranges is 80 to 105 °C.

Alicyclobacillus, Ferroplasma, Picrophilus, and Sulfolobus: All are acidophiles (optimum growth between pH 0 and 5.5).