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.