Microbiology and Nitrogen Cycle

Rhizobium (misspelled as 'Rhozobium' in the option) is a well-known nitrogen-fixing bacterium that forms symbiotic relationships with legume roots. Acetobacter is acetic acid bacteria, Mycoplasma lacks a cell wall and is not a nitrogen fixer, and Chlamydia is an obligate intracellular pathogen - none of these fix nitrogen.

Nitrification is the two-step process where ammonia (NH3) is first converted to nitrite (NO2-) by bacteria like Nitrosomonas, then nitrite is converted to nitrate (NO3-) by Nitrobacter. The specific conversion mentioned (ammonia to nitrite) is the first step of nitrification. Nitrogen fixation converts N2 to NH3, denitrification converts nitrates back to N2, and eutrophication is nutrient pollution causing algal blooms.

Rhizobia is “the group of soil bacteria that infect the roots of legumes to form root nodules”. Rhizobia are found in the soil and after infection, they produce nodules in the legume where they fix nitrogen gas (N₂) from the atmosphere, turning it into a more readily useful form of nitrogen (N). From here, the nitrogen is exported from the nodules and used for growth in the legume. Once the legume dies, the nodule breaks down and releases the rhizobia back into the soil where they can live individually or reinfect a new legume host.

Pea plant can fix nitrogen from air.

Rhizobia are soil bacteria that fix nitrogen (diazotrophs) after becoming established inside the root nodules of legumes.

This is the correct option as azotobacter plays the role of nitrogen fixation in nitrogen cycle.

Conversion of nitrate into nitrogen is denitrification; conversion of ammonia into nitrites and then into nitrates is nitrification; conversion of atmospheric nitrogen into ammonia is nitrogen fixation; and conversion of organic nitrogen within the remains of plants or animals back into ammonium by bacteria or fungi is ammonification.

Bacillus stearo thermophilus is thermophilic and its spores are killed by an exposure of compressed steam for 12 minutes at 121⁰C; therefore, its spores are used to test the efficacy of moist heat sterilization (autoclave). Other means to test efficacy of moist heat sterilization are chemical indicators, autoclave tapes and thermocouples.

Psychrophilic bacteria-bacteria that can grow best at temperatures below 20^oC, e.g., soil and water saprophytes and may cause spoilage of refrigerated foods.

This is the function of capsules, which enable many organisms to resist phagocytic engulfment called phagocytosis.

Without the constraints of the conserved molecule peptidoglycan, archaeal cell wall may be quite diverse. Methanogenic archaea possesses pseudomurein [Peptidoglycan like polymer which is cross linked with L –Amino acids].

 Correct answer- 2) Acetogenesis is a type of microbial metabolism that uses hydrogen (H2) as an electron donor and carbon dioxide (CO2) as an electron acceptor to produce acetate. Bacteria that can synthesize acetate autotrophically are called homoacetogens. Carbon dioxide reduction in all homoacetogens occurs by the acetyl-CoA pathway. This pathway is also used for carbon fixation by autotrophic sulfate-reducing bacteria and hydrogenotrophic methanogens. Often homoacetogens can also be fermentative, using the hydrogen and carbon dioxide produced as a result of fermentation to produce acetate, which is secreted as an end product. Anammox stands for anaerobic ammonia oxidation and the organisms responsible were relatively Annamox means anaerobic ammonia oxidation. This metabolism occurs in members of Plactomycetes (e.g. Brocadia annamoxidans) and involves coupling of ammonia oxidation to nitrate reduction. Annamox organisms are autotrophs and can fix CO2. Due to this property, these organisms can be used in industry to remove nitrogen in wastewater treatment processes. Syntrophy is the pairing of multiple species occurs in order to achieve chemical reaction which on its own will be energetically unfavorable. In Syntrophomonas, alone, the oxidation of butyrate to acetate and hydrogen gas is energetically unfavorable. But, when a hydrogenotrophic (hydrogen-using) methanogen is present the use of the hydrogen gas will significantly lower the concentration of hydrogen (down to 10−5 atm) and thereby shift the equilibrium of the butyrate oxidation reaction under standard conditions (ΔGº’) to non-standard conditions (ΔG’). Methylotrophy refers to the ability of an organism to use C-1 compounds as energy sources. These compounds are methanol, methyl amines, formaldehyde and formate. Several other less common substrates may also be used for metabolism, all of which lack carbon-carbon bonds. Examples are, bacteria Methylomonas and Methylobacter.

Bacteriostats are biological or chemical agents which stop bacteria from reproducing, but not necessarily harming them.

This is the correct answer as mustard is not leguminous.

This is the correct answer. Blue-green algae, apart from rhizobium bacteria, can fix free nitrogen.