Chemolithotrophy

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  • Chemolithotrophy is the oxidation of inorganic chemicals for the generation of energy.
  • The process can use oxidative phosphorylation, just like aerobic and anaerobic respiration.
  • the substance being oxidized (the electron donor) is an inorganic compound.
  • The electrons are passed off to carriers within the electron transport chain.
  • Generating a proton motive force that is used to generate ATP with the help of ATP synthase.

ELECTRONS DONORS

  • Chemolithotrophs use a variety of inorganic compounds as electron donors, with the most
  • common substances being hydrogen gas, sulfur compounds (such as sulfide and sulfur),
  • nitrogen compounds (such as ammonium and nitrite), and ferrous iron.
  • Hydrogen oxidizers – these organisms oxidize hydrogen gas (H2) with the use of a hydrogenase enzyme.
  • The aerobic and anaerobic hydrogen oxidizers exist, with the aerobic organisms eventually reducing oxygen to water.
  • Sulfur oxidizers – as a group these organisms are capable of oxidizing a wide variety of reduced and partially reduced sulfur compounds such as hydrogen sulfide (H2S).
  • The elemental sulfur (SO), thiosulfate (S2032-), and sulfite (SO32- ).
  • The Sulfate (SO42-) is frequently a by-product of the oxidation.
  • Often the oxidation occurs in a stepwise fashion with the help of the sulfite oxidase enzyme.
  • Nitrogen oxidizers – the oxidation of ammonia (NH3) is performed as a two-step process by nitrifying microbes,
  • where one group oxidizes ammonia to nitrimicrobe and the second group oxidizes the nitrite to nitrate (NO3-).
  • The entire process is known as nitrification and is performed by small groups of aerobic bacteria and archaca, often found living together in soil or in water systems.
  • Iron oxidizers – these organisms oxidize ferrous iron (Fe2+) to ferric iron (Fe3+).
  • Since Fe2+ has such a positive standard reduction potential, the bioenergetics are
  • not extremely favourable, even using oxygen as a final electron acceptor.
  • The situation is made more difficult for these organisms by the fact that Fe2+ spontaneously oxidizes to Fe3+ in the presence of oxygen.
  • the organisms must use it for their own purposes before that happens.

ELECTRON ACCEPTORS

  • Chemolithotrophy can occur aerobically or anaerobically.
  • Just as with either type of respiration, the best electron acceptor is oxygen, to create the biggest distance between the electron donor and the electron acceptor.
  • Using a non-oxygen acceptor allows Chemolithotrophs to have greater diversity and the ability to live in a wider variety of environments, although they sacrifice energy production.
  • Amount of ATP generated Just as both the electron donors and acceptors can vary widely for this group of organisms.
  • the amount of ATP generated for their efforts will vary widely as well.
  • They will not make as much ATP as an organism using aerobic respiration, since the largest AEO’ is found using glucose as an electron donor and oxygen as an electron acceptor.
  • Its much less than 32 molecules of ATP greatly depends upon the actual donor and acceptor being used.
  • The smaller the distance between the two, the less ATP that will be formed.